1) Syphon a decent amount of water into a bucket
2) Put fish in bucket
3) Scoop out gravel with clean tuperware, dust pan, etc...
4) Put in WELL rinsed sand. If you think you rinsed it enough, rinse it a few more times. Since you are putting your fish right back in the tank, you REALLY need it to be dust free before you put the sand in the tank so it doesn't cloud the tank.
5) Fill tank back up with new water like you would if you were doing a water change
6) Put fish back in tank
7) Monitor the water conditions daily for a week or so and do water changes as necessary
Has worked well for me on the 3 tanks I did. My big Hait went from a gravel tank to a sand tank, and he seems to like the sand just as well as the gravel. He takes big mouthfulls and spits them out after he moves to where he wants his sand. My old Dovii liked it too. He'd fan his tail to move the sand around.
It's sand only for me from now on. You're going to love it.