Speaker install

What exactly are you trying to?  Did a speaker go out?  Does your car have the factory CD changer or not? That matters because the cars that have CD changers have different speaker sizes on the rear deck (the cars equipped with cd changers have 6x9's on the rear deck.  The cars that do not have factory CD changers, which I happen to have a 97 Altima GXE that came with just a tape player, have 6 3/4 on the rear deck. 

You could try this link.  It has a pictured step by step removal of the rear speakers.  The car they demonstrate on has 6x9's, but it's the same process.  Let us know how that turns out for you

http://carstereohelp.com/stereoremovalNisAltRSpk.htm