My forum is acting up. Whenever someone clicks on the banner, old themes pop up, which i have deleted a long time ago. It's getting pretty annoying. Any help is appreciated!
http://tristsworld.forumotion.com/forum.htm

Can I have a screenshot of the theme before and after the change? I've clicked the banner (I presumed you meant the logo at the top) and nothing happened.

Hello,

I too have clicked the banner several times and couldn't reproduce.
It is to my opinion that the user maybe using extremely outdated web browsers, Such as IE5.
I suggest that you ask whom is experiencing this issue to confirm s/he is using a modern web browser such as FireFox 3.6.6 or Google Chrome.
If the issue continues to persist;
Ask them to clear the cache and cookies of the specified browser.

Also, have you recently attempted to use temporary themes or make a style (theme) switcher?

I did it normal way and it worked, weird.