Locate the gas tube release lever, it is on the same side of the rifle as the ejection port.

Flip it upward to unlock the gas tube.

Closed

Open

Now remove the gas tube.

To remove the lower handguard, locate the release for it. It is found here.

Pry it up with a knife or flathead screwdriver.

Flip it all the way toward the muzzle to release the lower handguard.

Push the handguard forward and then it will come free from the rifle.