The upper handguard is rotated off about the bore of the gas tube, just put a leather glove on and fix the portion that goes into the end opposite of the gas tube in a vise. Don't tighten it too much and twist 180 degrees and slide off. It may be difficult.
The lower handguard is removed by flipping a little "L" shaped lever on the handguard retainer to the rear and sliding the retainer towards the front sight/gas block. You may need to use a brass punch and hammer to get it started.