how do I change a upvc door lock barrel?

and how do I know the correct size to get?

Answers:
engineer has been the most helpful so far by the looks of it.....

Basically the same as he said..... Undo the screw inline with the barrel, there are very rarely any faceplates to take off on upvc doors!
Then put the key in, turn about 5-10 degrees either direction, pully at the same time, until the barrel slides out.
Measure from the centre of the screw hole to either end of the barrel (in mm), as both ends are not always the same length.
Then get to a LOCKSMITHS, it will be more likely that they will have the size you need and if they don't they can always get one next day delivery!
They start as little as £5 or 6, and go up to the mid £20, however the most common is around a tenner!
You will need to make a note of the shape of the cylinder, although 9/10 are euro shape (peardrop), there are odd doors fitted with oval and round (screw-in) shape cylinders!
Replacing it is just as simple.... turn the keys slightly, push the barrel through the door until it shows on the other side, then before trying to locate the screw hole, turn the key so that the bolt throws out about half way, that way there is no way that the cylinder can be out of position when you tighten up the screw again!

Good luck, hope this helps ;-)

Other answers:
GET A LOCKSMITH
GET A LOCKSMITH
Open the door, you will see a Philips screw that lines up to about halfway along the barrel.... take out the screw, put your key in the lock and rotate until you find the point that it frees... simple... now take it with you to B&Q they have several lengths available.... very easy to do...
Dead easy job. On most types just unscrew the philips screw/s on the side of the door and the barrel will push out quite easy.
Measure the length, offset of latch mech and type Oval or British - keyhole shaped.
Remove the lock by looking at the edge of the door, you will see a small hole, at the bottom of this hole is either an allen or pozi screw, undo this and the lock will pull out.

If you are unsure of the size, take the cylinder to the locksmiths, cost about £18 for a decent one.
you pick up a phone .. dial a reputable locksmith .. then wait ..
cha-ching! all done.
we had to do this, take the handle and the lock out, go to your nearest stockist, obviously someone will have to stay near the door while you or whoever goes to get it. ours cost £25 to replace, or you could get someone out, but they over-charge i think! its quite easy to fit even though it looks hard, hope you sort it!!
you dont a lock smith does
Speak to the supplier, if you bought the door in the last 10 years, you would hope for a free / low cost replacement.
locksmith should know
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