The front door lock in my UPVC door doesn’t appear to be locking ok any more. Sometimes i cannot get the key out and have to fiddle around for ages to open/close or get the key out. Ive tried some oil in the lock but doesnt appear to have made any difference so i imagine it needs a new lock. Can i get a new lock for these kind of doors, if so is it something i should be able to do myself or will i need to get someone in to do it? Any idea of costs would be appreciated too.