How can I make the helmet drop out of the player's slot and another one appear in its place?

Make a procedure that does the following:

• Sets a local itemstack variable to the item in armor slot 0 of the player. (Using the 'get item in armor slot' function)
• Set the item in armor slot 0 of the player to the new helmet item.
• Use the 'spawn item/gem' function to spawn an item, using the item stack variable for the type.