I have transferred tanks probably 10 times over the last few years between moving, setting up the tanks, changing spots in the house because the wife bought new furniture, and upgrading. It's not very complicated.
1) Get the new tank in place first. This may seem obvious, but the only reason this shouldnt be done is if it is going in the same spot.
2) have extra bins and water made up and ready to go. You'll need it, and you can use the new water as a "water change"
3) You can keep the sand if you want, but most people would start fresh. I have done both keeping and ditching the sand. Rinse the sand with a garden hose if you can to get as much detritus out as possible.
4) you may get a mini cycle if ditching the sand (only because you'd be getting rid of bacteria with the sand). I would get a bottle of Dr Tims/Microbacter7/Biospira to have on hand and add it once you're done transferring over. It's cheap and will give you peace of mind
5) You can keep the live rock and biomedia. As long as there is enough bacteria in those to process the bioload of the tank you should be fine. Again, get a bottle of bacteria if you're worried about it
6) Rinse the live rock in old tank water. You'd be surprised how much comes off of it, and that is less waste going into the new system.
7) Take your time. It can take a couple of hours to complete. Grab a hang on filter to run on whatever your livestock is in. This will give you as much time as possible to get the rockwork and equipment in place.
8) use two nets and be ready for fish to try and jump away from you. My hippo tang was the last one moved in the last transfer, he was hiding under a rock and when I moved it he darted 5ft across the tank and there was an audible "thunk" when he ran into the glass.
It took me 10hrs to transfer my 190 to my new 180 peninsula. All livestock lived. I actually pumped the water from one tank to the other and used a filter sock to catch anything.
