I just did this exact thing in my 75 gallon... I had some natural colored gravel and i switched it to black "Carib-Sea" Brand sand. A dozen LFS's and a few hours later my oscars were enjoying there new sand box.
My tips are... make sure all filters are off before transferring(only putting the sand in of course, not taking the gravel out). And if you have an extra tank, I would keep the fish in there during the process, taking half the water out of the tank and using it in the temp tank would be ideal, causing less of a mess during the switch. No matter how much you rinse, and you have to rinse quite a bit, you will still get clouding. But I assure you it goes away.
This will cause your tank to recycle in most cases, so being aware of this is also good. I use 2 Biowheel 350 HOB's so my recovery time was minimal due to the wheels having the proper level of nitrates.
Good luck on this, I am very pleased with my transition and I would like to say so are my fishes!