How do I change quantity?

On iOS:

After you've added an item to your cart, you may adjust the quantity on the Cart screen. Simply use the drop-down box next to your item to select the quantity you'd like. When you are done and ready to check out, tap Continue to Checkout to complete your purchase.

On Android:

During checkout, you may change the quantity of your order after you enter a recipient. Tap Add Recipient on the Checkout page, enter the name and address, and then tap Save. After you save the recipient, you may tap the + and - buttons to the right of the recipient’s name to add or subtract books from your order.