I upgraded from 60 gal
to 150 gal
at the same spot and here are the steps of what I did.
1. I used new substrate so I washed them first and set aside.
2. Next to my old tank is my dining table that I can slide on the carpet so I used it to temporarily move it there before setting up the new tank at the same spot. I did this by myself. If there is another person to help you out then you don't have to worry about lifting it and you just put it on the floor
3. I have 2 large plastic containers to accommodate my fish and corals and all the water so I placed them there with lights, heater and circulating pump while I removed the old substrate for disposal.
4. After moving the old stand and tank out of the way I placed the new stand and tank at the same spot. Set it up with new substrate including the LR
that would be at the bottom then run the pumps over night to give enough time for water to clear and parameter to stabilize. I mixed the old and new saltwater. I used 3 cups of old substrate to seed my new substrate.
5. The following day I made sure the parameter of the remaining water is closed to one in the tank (temp, salinity and pH) before moving the rest of the stuff.
So far it went smooth and my tank has been running flawlessly for about 6 months. I plan to add more LR
when the time comes with more fish and corals in the future.