Put a heat shield between the barrel and tank or just remove the tank (better) and lightly use a heat gun as suggested by 'enkey'. Don't know if the shroud innards are metal or plastic so be careful with heat.
The collar at the end of the shroud, closest to the receiver body., appears to NOT have a set / grub screw and is only a tolerance fit over the barrel. The shroud appears to have an inner collar that screws onto the barrel and that's all that holds it onto the barrel. Maybe that's too obvious.
Best Of Luck