first, get all your equipment together that you will need for the new tank.
clean the sand as well as you can.
do several large water changes on the old tank before the move.
use one of the empty tanks as a holding tank.
make sure it is clean/safe/not leaking. siphon out water from the old tank into the holding tank.
empty out more water until you can start taking out your rockwork. put that aside.
when rocks are gone and water level is low, start transferring fish to the holding tank. you can put the filter on if you want to.
once fish are all out, completely drain the tank and move it.
set up the 55, using water that is matched to the temp of the holding tank.
start with the lowest layer or two of rocks, then add sand, then add 1/2 water, finish the rocks and decor, finish filling the tank.
acclimate the fish slowly the same way you would if they were just purchased.
use both the old filter and the new filter on the new tank, for at least a month.
cycling should not be a problem.
notes - doing the large water changes beforehand allows the fish to adjust to the water conditions of the new tank, which will be straight tap water.
adding rocks before sand gives them a stable base, so if the fish dig in the sand the rocks will not shift.
using the old filter on the new tank keeps most of the beneficial bacteria. the larger water volume in the new tank makes up for the loss of any bacteria in the old substrate.