Subscription details and plan can be updated from the 'Purchases' page ,located in your profile menu.
If you wish to cancel a premium subscription - click the 'Cancel' option next to the plan details in the 'Purchases' page.
Downgrading a subscription from yearly to monthly is not applicable, in order to downgrade - simply cancel the yearly plan, and once it expires subscribe again to the monthly plan.
Note that premium membership remains until the end of the current billing cycle.
