Allie, it's not hard to do. There are 4 9/16s bolts holding the unit to the bracket. Or you can loosen the band and remove the small bolt on the bottom of the bracket. Unhook all the lines, and unplug the heater.
Once it's out, you can remove the dust cover from the heater (on the bottom). There is a snap ring inside that holds the plastic valve in place. The dessicant can on top spins off like a regular oil filter type. I would suggest removing that before removing the whole unit from the truck though. They are supposed to be hand tight only, but it seems that with age it feels like they were all installed by Hercules.
Clean that bugger out, wash everything well. New canister, and plastic purge valve...you should be good to go.