Best to determine the location of your title image, i.e. on this page it's
https://vborg.vbsupport.ru/images/cs...lue/vblogo.gif
Presumably it's similar to this:
http://www.yourdomain.com/forums/ima...etin4_logo.png
Once you figure that out you can simply replace the existing with your own logo renamed "vbulletin4_logo.png" by FTPing to your /images/misc directory.