First, make sure the rifle is unloaded, and then push out the takedown pin and the pivot pin and remove the upper from the lower receiver.
While pulling back on the delta ring tap the seam where the handguards come together on the edge of a table. When the handguards separate remove them from the upper. This may require two hands. If it is too difficult to remove, have another person separate the handguards while you hold the delta ring back.
The largest half of the MFT handguard goes on top. Note the orientation and where the groove in the back of the handguards will fit on the teeth of the barrel nut.
Put the front portion of the top handguard under the handguard cap, pull back the delta ring enough for the back of the handguard to rest under the delta ring. Then put the front portion of the lower handguard under the handguard cap and also pull the delta ring back far enough for it to rest on top of the handguard.
Now squeeze the two halves together until they snap all the way under the delta ring. If they are too difficult to seat all the way by squeezing them together use a plastic or wooden mallet to tap them into place.