Coupons

Hello, I setup my subscriptions in the membership plug in and I set up coupons... The problem I am having is I can not find were to get the two to work together... When ever I go to upgrade, the coupon does not work automatically. I have setup three membership One for Month, Quarterly and yearly... With 15% off quarterly and 25% off yearly... I would like for this to work on automation...
Thanks Tim