I want to change my lock barrel on our door as we have lost one of the keys. How do I go about changing the part over?
A very easy job to do yourself :)
To remove the lock barrel from your door simply remove the screw located on the side of the door that fixes it in place, then insert one of the keys and slowly turn it while pulling on the key quite hard. You may need to remove or slacken the handles to aid the removal of the lock barrel.
I actually copied this off a repair website where they sell Euro Cylinder/Lock Barrels.
good luck with it anyway.
P.S The website link is here: https://www.upvc-hardware.co.uk/locks-gearing/euro-cylinder-lock-barrels/euro-cylinder-lock-barrels
The website also shows you how to measure your cylinder so you can choose the correct one.