You only need to upgrade once you exhaust or about to exhaust your current backup storage. And email will be sent to you with the upgrade link.
If still want to upgrade or downgrade, Login to your dropmysite account. Open the link in the same browser. https://www.dropmysite.com/en/plans
Select the plan to upgrade or downgrade and proceed to payment
You will then be directed to the payment page. You can use PayPal account to make the payment and your account will be upgraded immediately.
Dropmysites's Support team is here to help from 9:00 AM to 7:00 PM SGT, Monday through Friday.
Email support@dropmysite.com and we'd be glad to help with all your questions