want to replace stock speakers, can it be done?

i want to replace my door speakers and the ones for the backseat, i know there both 4" and crappy, but i dont know how to swap them with some 4" ones from like best buy, b/c the connections look different,can someone tell me how to do this if it can be done by an ameteur! thanx

------------------
94 Z28,72k(auto/not red, but not purple)Mods!:

K and N FIPK
Flowmaster Muffler
Hotchkis Strut Tower Bar
Holley Airfoil
Hidden Shift Kit
Street Glow Pedals (red)
Sequential Turn Signals
Light Silver Badges
Kenwood CD deck w/ Remote
Massive 600 watt amp
2 12" Cerwin Vegas