Yes. Click Change plan from the Subscriptions tab in your account. You’ll be able to switch from a weekly plan to either a monthly, quarterly or yearly plan.
If you upgrade from a shorter-term plan to a longer-term plan, the change will be processed immediately and you will be charged a prorated amount, so you'll receive credits for any payments already made.
If you downgrade from a longer-term plan to a shorter-term plan, the change will be processed on the renewal date.