You can upgrade easily your plan from your client area : Services/My services, and click on icon 'Upgrade or via icon 'Manage' and see tab upgrade/downgrade). (note that update is immediate, and without disturbance)
For options, go to Services/Options, or by Services/My services, click on icon 'Manage' (see tab Addons).
You can easily cancel your services from your client area : Services/My services, see red icon 'Request Cancellation'
To change the billing cycle, please open a support ticket to Billing department.
For domains, click 'not renew'
To benefit from the 30 days satisfied or refunded, it is sufficient to request the termination of the service by procedure explained above, then to open a support ticket to the billing department.