The way members upgrade their membership depends on if you are using direct payment or not. Direct payment is a Pro System setting for the commission tracking tool where members are paid direcly. By default your system is set to "One Payment to Admin".
One Payment To Admin
By default, on the order page (your-domain.com/order) payment buttons appear where a member can upgrade their membership. You can also use the ~~ codes provided for pasting the buttons on web pages (capture/landing/etc).
To make a button for members to upgrade their membership create a button linking to: your-domain.com/admin/upgrademembership.php?id=NEW_MEMBERSHIP_ID
You will need to replace NEW_MEMBERSHIP_ID with the new membership id that you want members to upgrade to.
Get the Membership ID
Login to the admin account and go to:
your-domain.com/admin/memberships Then click on membership title to edit it.
Then copy membership ID from page URL as shown in the image.
Then replace us that number for the ID. For example if the ID was 2 your URL would look like: your-domain.com/admin/upgrademembership.php?id=2
With direct payment the Member is suspended untill he pays to unlock new membership.