Use it once a week for about three weeks. You can also use Reptile Relief to spray directly on the snake - using them both together is often the most effective way to treat them.
This article discusses one way to deal with them
And here's a helpful video!
If only using the PAM, it can take a bit longer to really work. Make sure the cage is not too wet, and again treat once a week for the next few weeks. They have a 30 day life cycle, so you want to make sure you are killing any new ones that hatch as well as any that might have been missed in the first treatment.
Hope that helps!
-Jen