Unregister GSAK (Help=>Unregister)
Choose this option to unregister GSAK
The GSAK license agreement (You know, that stupid thing that nobody reads but everyone accepts when installing GSAK) allows for the install and use of the GSAK registration on any computer you use.
However, This does not mean you can use your license key on your friend's/relative's computer so he/she can use it.
If you are going to give/sell your computer/laptop (and you have a registered version of GSAK on it) to another user please take this option before uninstalling GSAK