you could get one of those handy dandy plastic pocket things that clip onto the edge of the tank (the kind most fish stores use to hold a specimen after they catch it), and gradually acclimate with the new water, or just bag them in some water and acclimate them into the new tank like you just bought them...
but unless your tanks are drastically different, or it's a very fragile specimen, you don't really need much acclimation time when moving from tank to tank.