Of course you can!
1. Use your account to sign in our website
2. From the drop-down menu select "License Manager"
3. Click the "U" icon to unbind.
4. Follow the remaining instructions to complete unbinding process
When complete, you may let your friend bind this serial number to his/her account. Questions on how to bind? please refer to the following FAQ: How to bind my Gaaiho PDF Suite license?