One small size Phillips Screwdriver, if you dont know what that is you should probably not try to open your PSP, ok its something that look like this X
On picture 1 you will see the 5 screws that need to be removed to open the PSP, marked with red arrows. If you are not going to remove the whole inside of the PSP then dont bother to remove the 2 screws marked with green arrows. There is also no need to remove the whole label inside the battery compartment. I just did it for this picture.