A free way of doing this without the need for equipment is to float the transport bag in the quarantine tank for approximately 10-15 minutes before opening. This is very important to allow the temperature to come up and the ph to stabilize. If the bag is opened too soon, the fish could suffer ph shock. After the 10-15 minute float time, open the bag carefully and remove all but a third of the water and discard it. Every 10 minutes add ¼-½ cup of tank water. Continue until the bag is almost full, dump out ½ the water (discard it) and repeat the procedure until the bag fills again. Once refilled, remove the bag, net the fish and place in the aquarium.
Do not allow the transport water or any acclimation water back into the quarantine tank. Many LFS will use copper or other meds to reduce the instances of parasites and should be avoided. If possible turn off any bright lights and allow the new addition to adjust. This will greatly reduce any stress.