1) Go to the Manager Orgs and Subscriptions screen
2) Press 'Manage Subscription'.
3) Press 'Purchase Now' for the plan you want to subscribe to, which you will then be required to enter your credit card details for payment
Note: If you do have a voucher to enter, press 'Add Coupon' underneath the expiry date field before pressing 'Purchase' to confirm your credit card.
Note: You should now see confirmation of your payment success & your active plan.