I have TSR Workshop, but I don't get it. How do I edit the picture?

You should probably try their help forums, as they most likely have more users that know how to use it. Plus, isn't there some sort of help feature in it? Or their wiki? Also a bit more info on exactly what you are doing and what you need help with would be more useful.

I've never downloaded TSRW and have no idea how to use it. If you want to stick with that tool, as HL said, you're probably better off trying to get help over at TSR.

If what you want is an easy way to change the image on EA paintings though, and don't care which tools you use to do it, the tool set here at this site can accomplish that for you.

Just download S3OC and S3PE (stickied threads here http://www.modthesims.info/forumdisplay.php?f=604), install them, and go to this thread where I explained to someone else how to do it. It's very, very easy.

http://www.modthesims.info/showthread.php?t=391527

I can't speak for the ease of getting information over at TSR since I've never needed to ask there for any, but if you use the tools here people in the forums here will help you if you have questions about how to use them