i don't know where you can find proper instructions, but i can give you some info on removing the screen.
you first need to remove the button strip(for start/select/home etc) by carefully lifting the clamps on the sides and rotating the top towards you(if you're holding the psp like you'd hold it while playing the game)
once that one is removed(remember: don't disconnect the ribbon cable thingy, that needs to stay connected, same goes for the screen) you can carefully lift the screen starting from the top(you may need to use a little force, but stop once you get the feeling you're going to break the screen)
this "miniguide" starts from the point where you have the front of the shell removed.
this is all just own experience, since i screwed open my psp yesterday to fix the speakers which are hidden below the screen.