In your Members Area, Click on the Maintenance button on the left hand side and it will bring you to your Traffic Exchange Maintenance section:
Click on Site Maintenance this is where you add your sites and allocate your credits. You can manually add credits to your sites you want to promote,
or you can simply set it up for automatic allocation.
This will spread all credits evenly across any active sites you are promoting as you earn them.
Just switch allocation to ON or OFF whichever is best suited for you.