You have few options from which you can choose in order to license you copy of Sitefinity.
1. You can login in the backend pages of Sitefinity and go to Administration -> Version and Licensing, Activate new ( check the attached screenshot ) and browse to it.
2. Download the license for your version of Sitefinity and place it in App_Data/Sitefinity folder then restart the website.
If you have SF 3.7 license please contact our sales team
so you can discuss the options which you have.
All the best,
the Telerik team
Do you want to have your say in the Sitefinity development roadmap? Do you want to know when a feature you requested is added or when a bug fixed? Explore the Telerik Public Issue Tracking
system and vote to affect the priority of the items