Unplug the Skil router. Turn the router upside down and locate the collet lock, which is piece of steel with a cut-out area, shaped like half of a hexagon. When the collet lock is engaged, it prevents the collet from rotating.
Press the collet lock to to keep the armature shaft from turning as you loosen the collet nut. Pass the wrench through the space between the router's base and the motor and position it securely on the collet nut. Holding the router firmly, turn the collet nut counterclockwise until the nut is sufficiently loosened so that you can turn it by hand.
Remove the wrench. Once the nut in the collet chuck assembly has been loosened, continue to turn the collet chuck assembly counterclockwise until you are able to pull the collet free from the tapered armature shaft. The router bit can then be removed by gently pulling it from the armature shaft.