i dont know jack

[boxcarfan]

ok im good with engines and drive train...but i know nothing about audio...and i want to get a decent sound out of my car...02 sxt...how do i get the rear speakers out and what size are they? i got a 240 amp and i wanna get better speakers. so where should i mount the amp its about 9 inches long and 6 inches wide. and i wanna run RCA's to the back and in the amp. so would that mean i have to totally take power off the reg. wires going to the speakers now or can i just unplug it and run the RCA's....thanks for the help.