Spanner wrench and I believe a " feeler gauge " to set the barrel gap . Looks like you need to GOOGLE search Dan Wesson barrel changes .
You use the spanner wrench and take the nut off the end of the barrel inside the shroud.
Once thats done you remove the shroud and unscrew the barrel off the frame. When putting on the other barrel you screw it into the frame and use the feeler gauge between the end of the barrel and the cylinder, replace the shroud and screw the barrel nut back on.