At the quantity discounts tab you can manage the product’s current quantity discounts, view, change or delete them.
The current quantity discounts section:

The current quantity discounts section shows the product’s already defined quantity discounts and their ranges. You can change the min and max ranges, the discount (percent or amount), if the customer gets free shipping with the quantity discount and if a discount is available for wholesalers
The checkbox on the left indicates, if the quantity discount is active or not.
Press the save button at the bottom of the page to save the changes.
The add a new quantity range form:

After filling out the add a new quantity range form, press the add button to save a new range discount.