Well its not that easy , DPMS is notorious for using some kind of loc-tite on their Gas blocks & Hand Guards , but you might get lucky & it will tap off . You are lucky you are not using a continuous rail on the hand guard ( not that you will find one to match up to the Target height rail you have ) , because all you have to do is make sure you get a hand guard for a DPMS Gen. I Receiver & your good to go .
Sure looks like its a Carbine Gas system , but could be a Mid length . any 12" Free Float Hand Guard will work fine & can go longer , if you like it . There are a bunch of them out there & as said , not worried about which rail height , does make it easy .
Some kind of strap wrench will work to get the Hand Guard off , but may need to heat the Nut area of the Hand Guard up , to loosen any Loc-Tite up , if it won't turn with just the strap wrench . Just need "the Block " to hold the Upper Receiver for removal .
Here's a two 12" Hand guards , with Rifle length gas systems ,with added top rails , which you don't want & these's Hand guards don't come with them.