I had a 55 gal., then decided to upgrade to a 90, i finished it all in a day..it may be a very frustrating process because you may like the aquascape in your 55 and it wont be identical as the way it will look in your new tank, that was the problem for me..but you can do it in a day, in my case, i took all the water and sand out of the 55..added it to the 90 and then slowly added the fish through out the day..its going to take a couple of days for the new tank to look pretty again , since you will be moving stuff around, but dont worry, its not as bad as it sounds, good luck