Wait at least 20 minutes after the cycle ends before removing the spray arm from the dishwasher. The heating element needs time to cool down and may cause serious burns if you don't wait long enough.
Remove the spray arm from the dishwasher. Most GE Profile-brand spray arms are connected to the dishwasher with a nut. Twist the nut counterclockwise and pull the arm off of the shaft.
Submerge the spray arm in a sink filled with warm water and a few drops of a mild liquid dishwashing soap.
Clean the spray arm, particularly the jets, with a soft brush until all of the mineral deposits and other residue are removed.
Rinse the spray arm well under warm running water until all of the soap residue is removed.