Replacing a Double glazed door lock barrel

I have an intermittant fault with the lock on my Double glazed backdoor. the inside key at times jams and it will not turn without a lot of fiddling. I want to change it for a new barrel and thought it would be just a case of undoing the three screws, pulling off the handles and tapping the barrel through. However having only given it a gentle tap with a rubber hammer it will not budge, is there a knack to getting it out ?

Answered numerous times. Here's one a quick search threw up:
//www.diynot.com/forums/viewtopic.php?p=284651#284651

Yes, open the door and look at the locking mechanism, in roughly an area level with the bottom of the barrel you should see a philips headed screw, undo this, it'll be a machine screw thread like a bolt NOT a self taper, this screw retains the barrel.

Heres a pic of a barrel with the hole for the retaining screw to help you...

http://www.dgsupplyline.co.uk/results.php?category_id=11&sub_category_id=78&range_id=534#

Once the screw is out put the key in and turn to roughly 11 o'clock or 1 o'clock gently pushing on the barrel at the same time, once the cam lines up vertically it'll slide out no problem, see middle picture in the link to see the cam slightly sticking out

Bingo, thanks a lot, its easy when you know how.

Bob