The manual should show you pretty well what to do. I don't own a Daly pump, but from what I remember from a friend it is pretty much like all the rest. The nut on the muzzle end of the magazine tube should be hand tight, and when you remove it the barrel will slide off easily (barrel usually does not need to come off for this, but it will be loose and removing it will get it out of the way). The part I cant remember is if there is a snap ring holding the big spring in. If there is no snap ring, the spring will let you know when you have the nut unthreaded. If there is a snap ring you will need to remove that to get the spring and plug out.
Check out the book for sure, and if you are not sure, the dealer will take you through step-by-step of anything you need to not only do this but also anything else you might need to know.