The Quiz Center software can be used on one PC at a time but you might have a situation where you've upgraded to a new laptop etc and need to reinstall the software onto a new PC.
This is easy enough... there's two stages.
Stage 1 - Original PC
1. Go to the Quiz Centre on the current laptop - then go to the LICENSING section from the side menu. This is shown in the walkthrough video here (around 6m 20s onwards).
2. At the top there's a big button to deactivate your software.
3. Click this (you'll need to be online to do this...).
This will 'disconnect' your PC from your activation code.
Stage2 - New PC
1. Download the software from the email link you were sent originally onto the new PC.
2. Install as before and add the activation key again and it will link the new PC to your account.
If you have any problems with this then let us know and submit a ticket and we can help further.