Since it is the same water, just make sure the new tank is dechlorinated and the temp and pH is the same in both tanks. Once that's done, you can just bring the fish over from one tank to another. Don't move all the fish all at once. Just move about 2-3 fish per week. Do lite feedings in the new tank, perform water changes and lite gravel cleanings, by just waving the syphon above the subtrate to suck up the detritus. You don't want to touch/disturb the subtrate yet, since the nitrifying bacteria is starting colonize.