Editing navigation bar in K2

Hello,

My blog is located at http://www.karaboudjan.co.uk and I am running the K2 theme.

I would like to adjust the navigation tabs at the top of the page, on the header. This is what it looks like at the moment.

http://img22.imageshack.us/img22/7951/screenshot20100418at003.png

Due to the header image it’s quite hard to read the name of the page it links to. I would like it to have a background like the Blog tab has. I am having trouble finding out how to do this though. I don’t know what to search for. Is it easy to adjust?

Thank you for your help.