Discount on total price

HI, I need to add a function to my prestashop website. I want that A GROUP of my customers have some discounts when total order have more than 1000$, 2000$ etc.. 1000$ = -10% 2000$ = -11% 3000$ = -12% 4000$ = -13% 5000$ = -14% 6000$ = -15% Thanks in advance