When we got our 8 Discus, we were a bit nervous - they are a pricey fish. We knew our tank was cycled, and checked the temp and pH in hopes the waters were at least close to the same. It's probably a good idea to keep lighting at a minimum - no need for bright lights at this time. Gradually mix "bag water" with tank water.... Again, make sure the temperatures are close. I'm sure you know Discus like very warm water of around 85 degrees.
There's no special method to acclimation, but very clean water is a must for Discus.
Post again and let us know how it goes...