How do I re-rout after PayPal payment?

I have PayPal Pro Merchant Account, and I used that to set up the single payment PayPal gateway in the plugin. People are able to pay okay, but how do I get PayPal to re-rout back to the members area on my site once payment is complete? Right now it just stays on the PayPal site.

Usually I would create a button for this, but I can only provide the URL of the button image in the Membership plugin, and I can't seem to control how it acts.