Fix theme checkout conflicing issues with wordpress 4.1.1

Hi, I have a client site running wordpress 3.6 and using older version of theme. When I upgrade wordpress, it does stop working checkout as guest function so I need someone who can upgrade theme and wordpress to latest version keeping all functionality intact. Apart from that I need to setup credit card option alongwith paypal so maybe we can use [login to view URL] but not sure as I don't have time myself to sort out these things. Please only bid if If you are individual, not a company. Include "wordpress geek" at the top of bid so that I know you have read it fully. Otherwise I will just ignore your bid and report as spam. Thanks