how to change the barrel extension??

[skullworks]

It is an oberland arms AR-15. It is shitty brand that is made and sold to peasants in europe.

Since I am a "European peasant" this is of interest to me - especially since most U.S. brands are hard to get over here and/or they're severely over-priced. But back to my question; Oberland Arms make several models, hence my question which model this was? Was it a 16" Black Label, a 20" M1, etc etc?

BTW, Oberland use LMT BCG:s rather than the cheap Asian stuff you see in other European makes.