See attached link. The trimmer you have you have to buy the brushcutter assembly separate. You will just unhook the shaft and change it out.
Hold the outer part of the hosuing and turn the bump head portion clockwise to remove the spool assemly. You will then have to remove a few clips that secure it to the shaft. The head on you unit is not threaded on, that is why I am saying that you most likely will not be able to put a universal head with blades on it.