X-cart shipping change - Looking for xcart expert

Here is our site & the code change we need: Currently site is set up with a Free Shipping special offer for orders over $75. skin splendor .com / provider / [login to view URL] At one time, a free shipping coupon was set up, but we are not using this because we want the free shipping to be automatic for the customer; we do not want them to have to type anything in to receive free shipping. We need to set up the Free Shipping special offer so it only applies to orders being shipped using USPS. Orders using FedEx will need to always be $29.95, regardless of the cart total. Free shipping cannot apply to FedEx orders.