The full length plate may be secured to the PVC door by 8 or 10 screws but the lock barrel has to be removed first.
Remove the screws holding the inernal & external handle brackets then withdraw the square shaft
Now remove the screw below the dead latch. It's the thin one operated by the lock barrel/key.
Put the key into the barrel and turn key to 5 or 7 O'clock position to slide the barrel out of the lock.
The plate securing screws can now be removed and the entire lock prised gently from the door.
PS What's wrong with it, do you really need a replacement?
If so check make and model by putting multi point locks into web search
Ask again if stuck
Regards
Asanewt, February 2009
