There's certainly precedent -- Anne Rice's Vampire Chronicles switches main characters in its original trilogy: Louis in the first, Lestat in the next two. In that case, Lestat was a major character in the first book, so it made the transition a bit more smooth since we as the reader already had an idea of who this character was.
Since you say you want to kill off the protagonist of your first book and give the reins to someone else for the second two, there are several ways you can go:
Let the second person's POV dominate all three books. The main point-of-view character and protagonist don't have to be the same person. (Think John Watson versus Sherlock Holmes.) The current main character can still be the focal point of the story, but his tale can be told through the eyes of this second character.
Give the second person a strong presence in the first so that the transition to the second book isn't jarring. Since your reader knows the main character is dead, seeing someone else in the lead won't be a shock, and having it be someone they're already familiar with will help them to be more comfortable and keep you from having to introduce a new character.
Both of these assume that the two characters have some kind of relation to each other and are both present during the events of the first book, of course. Since I don't know for certain that's what you have planned, these may not work for you. If the second main character isn't directly involved in the events of the first, then you may want to consider:
- Bring back supporting characters from the first book as guideposts for the new main character. This is another way to give readers something familiar from the first book to latch onto and relate back to. This gives you as the author a chance to call back to the events of the first book and connect the narratives into a cohesive trilogy.
Switching main characters between books certainly can be done (and has been done), but you definitely need to examine why you feel it's necessary and how you are going to keep the books feeling like one complete story instead of separate tales that just happen to share a title.