Ok I had a revolutionary idea on this one.
1. I went to the vbulletin site
2. I found their support forum
3. I used their SEARCH FEATURE - yes some boards still have them
4. I got an answer
5. I got confused
Maybe it'll mean something to you:
I suggest if you can register a new account, then use tools.php from your DO_NOT_UPLOAD folder, upload this to your admincp directory and use it to give your new user account admin privialges. once you have done this, remove the tools.php then edit your old user accounts password
Hope that helps
Lux