From their site:
All information about you will be deleted, the uID profile will become inaccessible. You will not be able to log in with your uID account to websites with the uID sign-in system. Your e-mail will become available for registration. Your websites will be detached from this account but will not be deleted.
So, first -if you have them- delete the websites manually (or take for granted they keep existing). The creation of those pages is done by another company (free website hosting), and it’s quite easy to delete them: on the main/management page, bottom right, you’ll see the link.
Then when logged in, click the link named here. Top right gives you the tab (link) that says ‘remove’. Use it and there you go.