Game accounts? Why would you want to do that? You would need to know your current account number and write it down as you will lose characters in MP that you already have built up..............
However, if its cos you got banned from somewhere, most tend to IP ban you now, so it won't help out. Basically, note your ID number down, then uninstall / reinstall - INCLUDING the save games and MP account info - that way you get a new number etc. You can then change back by changing that number when you install again next time......

You won't get the the new ID even you reinstall FL.
I've heard FL reads the hard-drive's serial number and generate an ID. I don't think you will get an new ID without an new HD.
If you want change the serial number of HD though, don't ask me.

Strange, i know many a person who have changed MP ids without a prob, also the warnig of deinstall followed by install = no old MP saves there! Hence MICROSOFTS warning about saving your ID number incase you ever need it. If you UNINSTALL the game, it will generate a new one i am sure. If you delete or just reinstall it won't. Remove all traces of FL off of your H/DD and it WILL give you a new MP id number