the latch wont come out untill you have removed the knob as there is a spindle holding it in place,there might be a screw on the other side of knob or a round plate around the knob itself that you can prize off with a screwdriver then you will see the screws holding knob in place,take out these screws and the knob and spinle should come out and the latch will come out.Hope this helps
shaun www.sdwupvcrepair.co.uk, February 2008