CS6 IS version 8. If you mean one of the CC versions (9 or 10) which are only available by subscription it depends. IF your CS6 is a subscription license you may install the newer versions at any time. If it was a standalone perpetual license it cannot be upgraded without paying for a new subscription.
Thanks for the reply - what I currently have is not a subscription license, so I see my suspicions were true that I'm stuck with it.