Before you get started let the rod sit in a dry area for a few days, if it has been stored in a damp area, the bamboo in the male ferrule can swell causing a tight fit. Then;
Use the finest sandpaper you can get. Cut a strip about the width of the male slide. Rotate the rod in the sand paper a couple of turns. Polish the ferrule with 0000 steal wool. Let it sit a minute or two then try the fit. Repeat as necessary. Before you get too agressive with sandng the male make sure the inside of the female is clean, use a Q-Tip and acetone. Make sure that none of the cotton gets caught up insde the female. Work slowly, if you go too far you'll have more problems.
Pete