Start from here & choose your model & then type of accessory to add: http://www.apple.com/support/diy/

There will be a quicktime movie to show how to do, also another one for safety; re: potential static electricity damage, & also a pdf.

I used this page to find out how to do it for an early G4 not so long ago.

It's not difficult. I had some issues fitting it in properly but other than that. You may need to add a bit more pressure than they suggest but just making sure all the pins line up 1st. It didn't seem to fit in for me at 1st. lol I was sweating upon it incase I did damage b/c I know how sensitive they are both to static & pin damage. (yes I worked in electronics once upon a time. Ah it's getting close to easter time & april 1st)

OH hold on, I just noticed there's no iBook G3's on the list. You'll need to check with your local apple dealer to be sure you can add more ram. I just check Mactracker, & it seems the G3 iBooks only have one slot. But even the earliest has the ability for 300-500 MB ram & later to over 600 MB ram. So I guess you'd replace the old one with a large one.