If you no longer plan to use Geneious on a computer you should release your license from this machine. This can be done from the ‘Help' menu in Geneious ('Pro' menu in Geneious 5.6 and earlier). This will only release the license from that machine - it is not possible to release license activations from other computers remotely. Uninstalling Geneious from a machine will not release the license.
Note that there are a limited number of releases available within a given period of time and trying to release too often may be misconstrued as a user trying to share a personal license with others. Only release a license when absolutely necessary.