This article goes over how to activate a Socrative Pro license key. If you currently have Socrative Basic, this will upgrade your account to Pro. If you already have Pro, you can use the key to extend your current subscription.
To activate the license key, login to Socrative through the Socrative Website and click on your name at the top right corner and go to Profile (keep in mind, the account tab where you add the license is not available in the app).
In the Account header, you can view your account details. If you already have Pro, click on the Renew License button. If you're using the Basic version of Socrative, click on Upgrade.
Left: Pro user. Right: Basic user.
The link will expand into a new menu. Click on Enter License Key:
A new menu will show up to allow you to enter your license key:
Enter your license key and click Activate. Your account will be immediately upgraded to Pro.