This forum software gives the option to store this information in a database or cookie. Since this forum is so huge I can't imagine it running of the database so try clearing your cookies.

It could also be pulling it out of your temp internet files. You can either clear them or push Control + F5 to force a refresh. I'd recommend you clear them though so you're forcing a refresh on all the pages and not just the single page you control + F5 on.

- Brendan