Polarbackup stores the backup settings and the machine information in your (%appdata%\Polarbackup\Polarbackup). When you move to a new machine, this information will not be available there.
So now, when you download and install Polarbackup on your machine, and sign in to your account, if you have already reached the maximum number of computers*, you will be asked to delete or archive the older machines in order to be able to add the new machine.
The good news is that Polarbackup has a De-Duplication feature that will prevent uploading the same previously backed up files again.
* Polarbackup Home users can back up one (1) machine only, but Polarbackup Business users can back-up up to three (3) machines per user.