You can update or cancel your premium picks subscription at any time in Settings → Manage Paid Account on Odds Assist Pro.
The Manage button takes you to Stripe, where you can change your package or cancel your subscription.
If you cancel your subscription, you will have access to all premium picks until the billing period ends. For example, if you sign up for a weekly picks package on Thursday then immediately cancel it, you will have access to premium picks until the following Thursday.