More bass for a 98 Cadillac deville?

Hi for a while now Ive wanted to have more bass for my cadillac deville. Unfortunately i have no idea what to do when its come to putting an amp and system into the car and Ive heard that you may encounter problems when doing so in the cadillac deville and you need to keep the stock radio unit and hook up the new radio unit and all this other stuff. I don't know, all i know is that its confusing and might just be a waist of money and time. All i want to know is if there is an easy way to increase the bass in my car by replacing some of the speakers or something without me spending to much. Please list anything you can to help me out, thank you.