There are two ways to answer this. The first is that we do know that Hitler died in 1945. The evidence is overwhelming and conclusive, and there are no serious historians who doubt the common narrative of his suicide to be true. This includes eyewitness testimony and forensic evidence using dental identification. Yes, there are doubters, but they are almost universally conspiracy nuts who present an array of utterly disingenuous, not to mention contradictory, counter-narratives with little basis in fact.

That said, technology certainly has improved since the 1940s, and while the evidence already is conclusive, there are more tests that could be done today to cross those ts and dot those is if we really wanted to, although to be sure, I doubt that even having multiple, independent tests done by various DNA labs would actually change some of the minds of the nuts mentioned above. The problem is that the dental remains that we have are in the hands of the Russians, and they control very, very tight access to them, and will not allow testing to be done because they also have a skull fragment which is obviously not Hitler's but they continue to claim is, and they don't want that to be proven as a fake.

This is covered in much more depth in this podcast episode, by myself and /u/commiespaceinvader.