There is no longer the need to deactivate your license to move it to another machine.
If you're logging in with the same Redgate ID each time you install your license on a machine then you will never run out of activations as this only uses one entitlement.
If an additional user activates the same license, using their Redgate ID, this will consume another entitlement.
If you're having problems activating your license on a new machine it could be that you haven't logged in with your Redgate ID or that the ID doesn't match the one previously used. You may need to log in to the customer portal and free up an activation by removing an old user or removing the entitlement assigned to the wrong Redgate ID. You will need to contact the license owner if you can't see the license in the portal.