Utilize a tool to root. I found this to be the easiest. The only part that is somewhat challenging is getting your computer to recognize the phone, but it's like any other device you attach to your computer - you just need the drivers. Check out this link - it has the tool to root, etc. and all the instructions, links, etc. to get the drivers you need.
http://forum.xda-developers.com/showthread.php?t=1400871
Sorry for taking so long to get back with you. Once you have rooted, you can download the link to 4.04 and put it on your phone, however, just my own suggestion, look into doing the AOKP (Team Kang) roms - they have 4.04 and a ton of really cool functionality that is missing in any of the stock roms.
http://rootzwiki.com/topic/25590-build-36-change-log/
If you don't understand the terms, etc., just google them - it took me an hour or so to read enough to understand what to do. Now I am romming with the best of them!
Good luck and PM me if you need any further help! OH and BTW - the "super user" thing is what you get when you root the phone - rooting is just allowing you to have "super user" (admin) access to your phone...