Is this a student version or the commercial version?
I am not sure about how if it is the student version.
Being Creo 6, I am guessing you have a subscription, not a purchased license.
If you did not renew your subscription, you will need to get a new one that will give you access to Creo 7 and 8.
If it was a purchased license, then you will still need to get a subscription as that is the only licensing tool available now.