Depends on what language you speak. If you speak a form of English, your fears are generally unwarranted. I do not have specific figures for incidents of burn injuries or fatalities for the Axis powers or the USSR or France.
There are four different factors in play:
The first one is, in the long run, a bit of a non-entity. It very well may be that in any particular engagement, one tank or another may prove particularly tough. For the ultimate sort of example, King Tiger in 1944, or Matilda II in 1940. However, wars are not just particular engagements, and especially for the german side, the longer you hang around, the more chance that the odds will catch up with you. And, of course, you only get to die once, so if it happens in your first engagement or the 40th, it doesn't make much difference in the end. To this end, what matters is the overall survival rate of a tank crewman to the end of the war. Most German or Soviet tankers of the war seem to have been lost. Between 3% and 6% of US tankers were killed, an additional 9-18% injured. (These figures compare very favourably to infantry). Official figures are the lower end (3% and 9%), but /u/the_howling_cow has done some interesting extrapolation on non-armored force branched tank crew casualty rates. On the other hand, according to the director of the Panzermuseum, some 300,000 out of 400,000 Soviet tankmen were lost. That indicates a pretty low survival rate.
This tends to vary a bit by type, but as a general rule, almost all tanks in WW2 seemed to have a burn rate somewhere between 65-85%. More likely than not, if your tank is knocked out, there will be a fire. Partially this is because us tankers don't like taking risks: If we aren't absolutely sure something is dead, we'll shoot it again, until it catches fire or changes shape, because those are the two very obvious giveaways that the tank is no longer a threat. Also, a tank which has burned out is far less likely to be repaired: If for no other reason, than the integrity of the armor is lost, so there is further reason to keep shooting. This does not, however, mean that the crew are in the tank all this time. They usually will get out after the first or second penetration. The significant change came with the late-war M4 Sherman and the M24 Chaffee, which introduced 'wet stowage'. This was liquid protection around the ammunition so that the burn rate of the tank dropped to under 10%. (It is worth observing that the primary cause of fire was ammunition, not fuel).
Several factors come into play here as well. For example, Dmitry Loza, in his book about commanding M4s observes that because of the difference in the nature of Soviet and American propellant, you usually had a couple extra seconds to get out of a Sherman before the fire became a total conflagration than you did in a T-34. Further, tanks can be easy or difficult to get out of. I have started, in my videos, to occasionally do the "Oh bugger, the tank is on fire" test, to see how long it takes for me to get out of the hatch. A Sherman is dead easy. A Comet or Panther, less so.
A US Army Surgeon General's report in 1945 indicated that of all US casualties, burns to tank crewmen were for 3-5% of them. And a third of those came from mishandling of gasoline, so presumably they were outside the tank when they got burned (Eg refuelling a tank on a hot engine deck). Things are less rosy if you are British, with a document written in 1946 " "A survey of casualties amongst armoured units in NorthWest Europe", with the statement that some 40% of their non-fatal casualties suffered burns (Of course, the British also had a wider variety of tanks with differing characteristics and also differing loadout policies). Of that 40%, 15% were also injured physically by something else, and thus 25% were burned only.
So, to summarize:
First, you have to be in a tank which is hit.
Second, it has to be a tank which catches fire when hit, which in fairness, is most of them, unless you're in a later American tank.
Thirdly, you have to be one of the one or two (In British or American tanks) members of the four or five crewmen in the tank to suffer an injury.
Fourthly, even if injured, you seem to have a better than 50-50 chance of not having to worry about being burned if you are British, and an astonishingly high 90%+ chance of not burning if you are American.
Fifthly, if you are burned, there is a very small chance of burning being the cause of death. You may die burning from other causes, which is hardly a comfort, but it won't be burning to death. The US report indicates that the average US tank crew casualty was in a hospital between 30-120 minutes after being injured. (That means going from the tank to immediate treatment, movement to an aid station, stabilisation, then transfer by ambulance to hospital). The US medical system was astounding and doubtless many casualties which may have been fatal to other militaries were not for the US Army.
As David Fletcher observed, there is something primal about the fear of being burned and thus a few observed incidents will have a huge psychological effect. The US report observed "The psychological effects of burnouts have been quite uniformly bad. Two or three burnouts appear to be the maximum tolerated by the average man. A very few have stood six or eight without breaking, especially when two or three have occurred the same day" (Which says something about the survival rate if the crews were able to hop into three different knocked-out tanks in one day). The British report stated "Many tanks suffered major damage by fires which did not injure their crews".
Overall, then, the answer to your question is "not very"
There is a fairly comprehensive answer here from a thread last year that goes a long way to answering your question as it pertains to the US Army. The answer is by u/the_howling_cow based on some sources listed at the bottom as well as a very insightful video by u/The_Chieftain_WG, who in turn compiled the information in his video based on a variety of sources.
This data does not provide the exact answer - "how likely am I to burn to death", but it does provide some related data like the number of casualties in burned tanks vs non-burned tanks. Some key points:
One consideration that uThe_Chieftain_WG loves to go into in his videos that doesn't get talked about much is the ease of evacuation from a tank. The Sherman tank is extremely easy to get into and out of quickly compared to most of it's WWII contemporaries.
Regarding tanks burning, the Sherman was not worse than other common tanks that did not garner reputations for burning, e.g. the Panzer IV. The Chieftain notes that "number of tanks found burned" is not necessarily a good metric to calculate the number of tanks that burned when they were first hit, because deliberately continuing to fire on a tank until it caught fire to render it irreparable was a noted phenomenon.
As such, you should expect that if you were a US tanker at least, you should not be particularly afraid of burning to death. Total deaths were low, most tanks did not catch fire immediately upon being struck, and casualties among burning tanks was still only ~26% which includes the number of casualties that were not caused by the combustion.