You can do so online:

Just logon www.drivehq.com, click on My Account --> Subscribe --> Current Subscription.

You can then select a subscription service and cancel it.

Please note you must delete your files; or if you are a group account, you must delete sub-users before you can cancel your subscription.

Please note DriveHQ customer support generally doesn't support service cancellation, unless you have really tried and have difficulty cancelling by yourself.