If you can aged the water (new s/w circulating with heater, match the temp) in new tank (about 50-70 G) along with new substrate, then fill with water from 55G. If possible reuse the substrate by rinsing them in few inches of its own water then move them to new tank. With this method, you can move the fish into buckets with water from 55 (make sure that temp dont drop in bucket/holding container). Reuse any deco/LR from 55G 9no cleaning no matter how dirty/filthy it may be, could do that once tank is well established), you can always take them out if you wish once tank is well stablized. Once the transfer is complete, start acclimating fish to new tank water. Make sure to RUN the filters from 55g w/o any cleaning/changing. If need to top off, just prep new s/w to do so.
Once fish are in new tank, monitor the water closely as may go thru
NH3,
NO2 spike.
If see spike, control it by small water changes and cutting down food. If you have enough LR in 55 G , very unlikely that you will experience such spike.