You can change your application's plan by going to your application's editor, clicking on Settings, then on the App Plan tab, and clicking “Update plan”. Once there, select either the monthly or annual billing frequency, then select the plan of your choice and click the button at the bottom of the confirmation popup to confirm.

Note: For some users, the plan change option may appear as a dropdown menu.
​
Upgrading or downgrading a plan part-way through the billing period will result in your account being credited for the unused time on the plan. Please note that when downgrading to Free, your app plan will stay active through the end of your billing cycle (and will continue to consume workload units), thus no credit will be issued.
​
Please note that the Annual subscription is charged in full for the whole year at the time of upgrade, and billing frequency cannot be changed back to Monthly once the Annual subscription is active.