do i have to remove the barrel to remove the retainer ring  ( push down collar at the base of the forearms) or is there a trick . I have no front post  so can i slide it forward? I have really have no access to a vice so removing the barrel is a last resort. Hell i'd rather take a  dremel to it and cut it off , lol.

Are you referring to the Delta ring assembly?  When you push the delta ring back to remove the hand guards take a look and you'll see half-moon cuts all the way around the inner piece.  That’s the barrel nut.  There is a wrench that you'll need to loosen the barrel nut, [b]but you'll never get it off unless you have an Armorers block to hold the receiver in a bench vise.[/b]  
Once the nut has been loosened you can unscrew it and pull the barrel off. You can pull the snap-ring off the backside of the delta ring assembly to remove the delta ring and leaf spring.  This will leave you with a bare barrel with just the barrel nut on it.  If you don’t have a front sight base you can skip taking apart the delta ring assembly and just slide the whole assembly off the front of the barrel.

A 9mm barrel is easy to change out cause theres no gas tube to worry about.  Have fun!

so removal of the barrel is a must to remove the ring. The reason i am asking is i purchased a  fre floating forearm w/ rails to replace the M4 grips i currently have. i have not got them in the mail yet but from the pictures on the sit i do not see that ring. I was hoping i would not have to remove the barrel  like i had to when i made i a flat top.but if that's the only way i guess i'll have to. Thanks