I actually answered a similar question a couple of months ago, here

/u/FamousByVictory /u/Sn_rk I figured I’d just tag you guys too.

And to expand on the question of whether or not an emperor could just disband the guard without fear of repercussions: no, they could not. Flavius Valerius Severus attempted to disband them, and they immediately proclaimed Maxentius, the son of the retired Maximian, as the new Emperor. As my linked answer explains, Constantine was able to disband the guard because he defeated them in the battle of the Milvian Bridge.

Edit: my linked comment should say that Constantine defeated Maxentius at Milvian Bridge.

Follow up question : Is there any record of Praetorian Guard doing their job ? Like saving the emperor from assassination

Follow-up: Could the emperor just disband and abolish the guard (without having to fear repercussions)?