In Avant Browser, go to Tools >> Avant Browser Settings... >> Clear Records (tab). Now look for Temporary Internet Files. This is your cache. You can check it's box and check the bottom box so it will automatically erase your cache when you close AB. You can check all the boxes in that tab if you want to be completely "safe", however, you will have to log back into VirtualTeen forums everytime you reopen AB (because the cookies would be deleted every time AB closes).
If you don't feel comfortable with doing all that junk, then you can just go to Tools >> Clear Records, and clear whatever you need to (including all records).