How do I properly create subscriptions in WP Membership?

I am creating a membership site that has three registered levels: core, pro and founder.

Core is free and people can stay at this level indefinately unless they want to upgrade.
Pro and founder are both paid levels.

What I would like to happen.
When someone registers for the Core (free) level I would like them to see the option to upgrade to the founder or core level in their account page. How do I make that happen?

Thank you.