how do you unequip an item from a pet

It's been a few hours since you've posted this, but in case you still need it:
Got to "Account" > "Inventory" > "Switch to Equipment"
From there, you'll have to manually find the pet you'd like to remove or add equipment to.
Just drag and drop from the pet slots to your inventory to remove, or from your inventory to your pet equipment slots to equip.