If you have existing members in your membership and want to provide the facility for these users to upgrade their levels or packages, this can be done following the guide below:
For Paypal Buttons (Standard PayPal)
The best way to handle this would be to create a subscriber modification button. To do this, go to OptimizeMember > PayPal Buttons > PayPal Subscr Modification Buttons.
From here you can generate a shortcode which will create an order button for a package upgrade.
Once you have generated your order button code, this would need to be added to a page within your membership where your member is already logged in. This should also be possible with a normal paypal order form if you wish.
For PayPal Pro-Forms
If you’re using PayPal pro forms the option is located inside:
OptimizeMember > PayPal Pro-Forms > PayPal Pro Billing Modification Forms.