First, before cancelling please consider your reasons. If you have a billing or support issue we can help you with please put in a ticket. If you need to change the domain name on your package or the size/price of your package we can assist you with this without cancelling your account.
To cancel your hosting (not domain, just hosting) please log in to the portal. Any invoices that have already been generated must be paid before cancelling your account.
Click on My Services
Click on the icon to the right of the service you wish to cancel
Scroll to the bottom and click Request Cancellation
Fill out and submit this form. The system will automatically cancel the package at the time you specify.