Vbulletin update & customized template update

Vbulletin specialists only. If you do not have experience working with Vbulletin 5.x.x please do not bid, thank you.

I am currently running 5.4.4 but need to upgrade to 5.6.4. Which I could do myself – BUT the theme/template that I am running as well as related css has been customized. I do not want to lose the customization please.

The website is for a non-profit organization, so we are budget conscious.

Regards,
-Mike