Is it possible to upgrade licenses from 5.5 to 6.0 having only active subscription services without support services?
you can upgrade your license when you have an active SnS (Support and Subscription). As this is one contract I'm not sure how you can only have one of those.
The easiest way is to go to the MyVMware portal and check if the update is available for your license.
See here how to do it: