Depends on what type of freefloat because there are a few different setups, but to make this as simple as possible;
Make sure unloaded and remove bolt carrier. I like to remove the carrier to ensure that no forward pressure is on barrel from the carrier and buffer so it doesn't try to push the barrel forward when the delta ring is removed and just seems safer to me this way. Especially if your upper has a lot of excess room where the barrel extension pin goes.
Remove existing handguard (top and bottom):
Remove flashider (if applicable)
Tap (drive or beat :-D) out the taper pins from the front sight and front handguard cap and pull off the muzzle end of barrel. (Usually from the left to the right if installed correctly, but depending on who put it together could be different but you can tell by looking that the thinner side of the taper pin should obviously be the side you should hit with a punch to remove)
The gas tube should also come out with the front sight so try to avoid twisting it too much so you don't bend/warp it.
Unscrew Delta ring with an AR multi tool and slide off the muzzle end of barrel
Screw the new barrel lock nut onto the reciever (this is what holds the barrel in place to the upper) and index the new handguard if it has rails, or if a non-railed tube, just tighten up with a strap wrench until very very tight.
Reinstall the other parts that you took off in reverse order. (The old handguard, delta ring/springs, and front handguard endcap won't go back--just put them in your spare parts box).
If you're wanting to get rid of the front sight and use a low profile gas block, you'll either have to tap out the roll pin in the top of the existing front sight and re-use it and the gas tube, or buy new ones with the low profile block you're wanting.
To install, just try to line the new gas block with the gas port hole and tighten it down depending on the manufacturers specs. A good way to check (tune) the alignment is to plug off the chamber with a foam earplug stuck in the chamber and blow into the muzzle while feeling of the gas tube hole while in the reciever. When you get the most air pressure coming out of the tube, the gas port is lined up
. I'm sure there is a more scientific way to tune the gas port hole alignment, but this works and is completely free except for the cost of the earplug :-D
This is essentially the same directions to swap a barrel also.
