First off it is not a good idea to mix crushed coral and sand, they will work against each other, the cc will rise to the surface and the sand will work its way to the bottom and you will still need to vaccum the cc to get the waist out, cc makes for a poor biological zone, go with all sand, much better filter.
As far as chainging:
Step 1: Remove any existing rocks, corals, fish, and other inverts to their temporary homes using the existing water from the tank, and some of the water left if possible. Make sure that any existing filter material containing your bacteria bed be kept wet and circulating if possible, this will help prevent severe spikes from the change, or at least keep them to a minimum.
Step 2. Stir up and remove the crushed coral. This can be a mess depending on how your CC was maintained; there could be plenty of evil waste and fouled water here. Now here if you wish or need to you can save some of this CC to seed your sand bed by placing it in nylons and making some CC nylon balls 6 or 8 should be plenty.
Step 3. With the tank empty its time to do a complete cleaning of the inside of the tank, scrape off that old algae, check the silicone seems for any problems.
Step 4. My preference here is to place a layer of egg crate down on the bottom of the tank making sure that it is still an inch or two away from the sides of the glass. This way the egg crate will help to prevent any reefalanche that may happen. Some will build a PVC stand to place the rocks on so that the sand bed will not cover several inches of expensive live rock. Others will use cheap base rock and place the live rock on top of that.
Step 5. With the egg crate, PVC stands, or bare bottom tank in place. Place a layer of sand down, about 1 inch. Then start to aquasacpe using your rocks that you will place on the bottom of the sand bed, twist the rock in a little to help stabilize it. Then pour the rest of the sand in.
Step 6. Slowly add your water, the speed at which you do this may depend on if you have some corals in the first pieces of live rock that you placed in your tank, but for the most part the slower the better, this may help to reduce cloudiness.
Options include using all dry sand, all live sand, mix of both. If you can get your hands on the Southdown then that is what I would use.
Just wanted to throw my 2 cents worth in.
Thomas