Sorry, but its not QUITE that easy, they don't take anything like a normal wrench. There are "special" wrenches for that purpose, but I've removed and replaced many over the years (owned Mossberg 500s for 35 years.)
I usually just take a screwdriver, put one layer of fabric(like a shop rag) over it, and "tap" (in one of the 2 grooves in the forearm nut) it 'til its loose enough to remove by hand. Doesn't take much. Use the same technique to tighten (not much force required).