Need to change the Vbulletin header to my own

[rin]

These are basics of HTML. Exactly why are you running a website and don't have a webmaster to do this work for you then?
Use something like Filezilla to upload the image to any directory.
Find out the full path to the picture and then replace the old path with the new path.
Alternatively, you can just replace the old vBulletin image with the new one.