Once you have the 3-point door lock apart, this shows you how to remove the existing barrel.
First, put it in the 'unlocked' position. Remove the cast guide section (note which way it comes out). Turn the barrel with the key till the two square sections of the barrel line up with the two square sections on the barrel housing.
Note the spring-loaded tongue. Push in the tongue with a small flat-bladed knife or screwdriver.
Pull on the key and the barrel should slide out through the front.