How do I de-register my old Mac?

I’ve bought the personal edition registered on 2 Macs. I’ve just got a new MacBook and want to deregister the old laptop and register the new. How do I do that?
Thanks for your help,

Access License Management
To access the Blocs license management settings, login to the UI Store ( and from the main menu at the top of the webpage click the link labelled My Products, this will take you to a section containing all of your purchases made at the UI Store. Navigate to your order for Blocs and click the red link at the far right labelled View Licenses. This will take you to the license information section where you can obtain your license number, check its status and also manage its uses.

Excellent - thanks for your help…

my pleasure.