Well the nice thing is you are only moving a smaller tank.
1. Get ya a 20 gallon tub of some kind or a tote
2. I would drain all the water into the tub except enough to keep sand alive and keep the fish submerged
3. Get ya a 5 gallon bucket with fresh saltwater, as you remove each piece of rock dip it in the fresh saltwater to clean off any debris.
4. Place all the rock in the tub, then remove all fish and corals and put in tub as well
WARNING!!!!!- when removing rock be care to try not to stir up sandbed very much
5. Make sure you have a heater and small powerhead in the tub
6. Remove sand into 5 gallon bucket and rinse clean , However if I were you Id simply go buy a couple bags of new sand
7. Set up 75 gallon as you normally set up a tank, then place rock , fish and corals into new tank.
I did this when I went from a 65 to a 150 about 2 years ago , I had a 40 gallon tub I put everything in it for 2 days and took my time setting up the new tank, nothing lost and never had a issue.