You can cancel at any time in the Gold Nitro dashboard on the Account page. Click the "Cancel Account" button and follow steps to cancel your account.
Note that canceling your account immediately stops all automated activity and future billing. At the moment it is not possible to delete a Gold Nitro account.
If you're using auto follows and are canceling, remember that canceling also turns off auto unfollows. You may want to turn off auto follows for 3-4 days so that we auto unfollow everyone we followed first. You can then cancel afterward.