how to go about this?

how would i go about changing the ratio of the rear axle? what parts would i need to replace and off of what kinda car? i own a 85 caprice 305. i hope my questions clear because i just read it over and it might be kinda confusing?

Basically, you just simply change the pinion and ring gears in the differential.

Basically, you just simply change the pinion and ring gears in the differential.

what year / make car would the pinion / ring gears come out of?

You have to do some research on what you have. Likely you have a 7'5" ring gear knowing what you have, but you can verify this by looking at the SPID information. Up to '84, the SPID information was on a paper attached to the top of the gas tank (you have to drop the tank to see) but beginning in '84 they moved this information to a sticker on the underside of the deck lid (Service Parts Identification - DO NOT REMOVE) - you want to see what 3-character alphanumeric identifier you have that starts with a "G" (i.e. G80, GU4 etc). Post what you have here. G80 is limited slip (Positraction) and I believe these were all 8.5" but I could be wrong.