is changing battery a DIY job?

[frosty]

car is a 1990 190E with an interstate battery (that I got almost 5 years ago)

okay, I kinda knew something might be up with my battery because the past week it has been cranking as if there was not enough juice in the battery...you know that sound and feel of the crank? well, I thought it might be the battery going out. the temp has been around high 50s to 60s deg. F and it has been raining here. earlier today I went to start the car and it cranked but did not fire, did it again, and that's when it no longer crank, and I thought it might be the battery. I went to get the portable jump-start kit and jumped the car. it fired up. so my suspuicion was confirmed; it seems the battery may no longer hold a charge. now I think I may need a new battery. DO I NEED A NEW BATTERY? or can I just charge it up and the battery is all good again? interesting that I had this experience almost 5 years ago, and this interstate battery I have now says it is pro-rated with a 60 month warranty!

anyhoo, if I do need a new battery, can I change the battery myself? is it what I think it is: just disconnect the pos. and neg. wires and have my radio codes ready? I can do that. or are there some other electrical/computer wires hidden somewhere that I have to also mess with? I'm not too thrilled about taking it to the shop and--if I remember correctly--have them charge me over $100 (was it $170 something) for a new interstate battery. I might get a generic battery if its cheaper.