Just do it
Just get some big buckets and do it. If you have old gravel and live plants forget about cycling issues, just move everything over.
Remove fish and heater and filter if possible and a few plants to a large bucket of tank water (20 gallon rope handle from Walmart) and cover with netting or something to keep in fish jumpers. Add Prime or Amquell or such to the bucket to help with the crowded situation, best to not feed for a day or so before this. Add a sponge filter if you can.
Drain tank. Save water as possible. Aerate filter media.
Remove the top 3/4" layer of gravel and retain in shallow pan just covered with tank water. Move lower gravel to new tank, add new gravel as needed then top with top gravel that was saved -- this retains the bacteria that live in the surface 3/4 inch of the gravel without mixing that with lower anaerobic levels of gravel. At that point you may want to add some water to the tank then drain it by using a sphon that is put into a depresion so it drains all the way to the gravel, that will suck a lot of the dirty water down into the gravel.
Fill part way with old water or dechlorinated new water, replant and decorate, Fill to a few inches from top, start filters (maybe with extra floss that can be tossed out when it has cleared the water of dust and such). Put in fish, fill to top, turn off lights and come check on them all tomorrow.
That leaves the old tank empty. If that is not the idea, then run a new filter on the old tank alongside the old filter. After a few weeks, set up the new tank with new gravel and stuff, move one filter and half of the fish and half of the plants.
No cycle problems, either way, but you should test daily to be certain, and feed very lightly. I'll bet you don't test any ammonia at all, ever.