1) Fold down the tops of your uggs on sale to more easily reach the inside bottom of them. The more you fold the better, as this gives you more visibility while working on this project.
2) Use a utility knife to cut a "C" in the heel of the insole, along the sides and back of the boot. Cut lightly and don't cut through the outer material of the boot.
3) Use the edge of the knife to peel back the heel of the boot's insole. Don't tear the fabric or any other material as you pull away. Do not separate the material completely from the inside of the boot. Use a shoehorn or similar object to separate the lining from the bottom of the boot without tearing it open.
4) Slide the insole with arch support into the boot between the lower lining and the sole. Use a small amount of adhesive to hold the insole to the floor of the boot.
5) Use adhesive liberally on the underside of the heel material that was cut away initially and replace it. Place a heavy object in the ugg boots on sale and allow the adhesive to set for 24 hours before wearing your Ugg boots for any extended period.