How should I clean my Wilfa grinder?

The owner's manual for your specific model should have good instructions. There are good tips and videos online for other grinders, but I don't know how well they apply to yours.

The general idea is to gently remove the hopper, bin, gasket, and similar parts, and remove whichever side(s) of the blades are designed to come out. Vacuum out the coffee dust, then use a small wire brush to loosen more coffee grounds, and vacuum again.

A thin wood kabob skewer is a good tool for cleaning the corners.

The hopper and such parts are probably washable. Do not get water on the grinder blades unless the manual says that's OK.

I have not used cleaning pellets but I'm skeptical that pushing additional stuff through will clean out the accumulated dust and oils from the path. If you do try pellets, follow them with some coffee beans as a "chaser" to minimize the pellet dust in your next batch of coffee.