Can I Upgrade and Only Pay the Difference?
You can upgrade any time.
Because MemberPress is an annual subscription, the cost of the upgrade is pro-rated. So the sooner you upgrade, the more that is applied toward the upgrade.
Upgrading is simple in MemberPress. If you decide you'd like to upgrade from the current version you are on, simply log in here, go to the Subscriptions tab. Then go to the far right of your Membership and click the Change Plan link.
That will send you to the standard MemberPress purchase page, but the prices you'll see are prorated based on what you've paid already, and how long you've had that membership. So, the sooner you upgrade, the more you'll be credited.
After clicking the Get Started button on the edition you'd like to upgrade to, you'll be taken through the basic purchase process again.
For more details on the upgrading process, please visit this page.