Rear door lock issue

Hi

I have started to get issues with my rear drivers side door lock

Sometimes it will lock and sometimes it doesn't, also sometimes I cannot open the door from the outside or the inside.

I also have problems with the window coming down slightly(about half an inch) and when you first start driving the dash flashes up as though the door is open, the door lock button on the drivers door flickers and also the button that locks the rear windows from opening flickers, this probably happens for the first 2 or 3 miles and then stops, plus the alarm can randomly start going off after the doors are locked.

I am hoping this is down to the door lock as I have now got a replacement, does anyone know any good instructions of how to change the lock (including video or photo's)

Thanks