You have to log in to the control panel with your Hostpoint ID. Then click  in the menu on "Domains" and on "Edit" to access the domain administration.

You also have the option of setting a domain to inactive by deleting the nameservers that are set. Your domain will no longer ‘function’, but you remain its owner until you cancel the domain.

Note that the final change of name servers can take up to 48 hours after the new servers have been entered.