Membership (subscription) upgrading

[imsandertjeee]

Hello,

On my community we have 2 subscription plans..

PRO membership (lets say 10$ / lifetime)

PRO+ membership (lets say 20$ / month)

The PRO+ version is an upgrade version of the regular PRO membership.
Some people buy PRO first, and want to upgrade to PRO+ later..

Currently is is impossible to upgrade from PRO to PRO+, is this because one is lifetime and the other is monthly?
It should be possible to upgrade to a different membership and after that is running out then revert back to PRO membership..?

How can this still be done?