You have to field-strip the gun first, and then comes the (very) hard part: You have to remove the metal inner receiver from within the plastic grip-frame.
The retaining spring fits into a recess on the side of the inner metal receiver, between it and the plastic grip-frame.
For really good instructions on how to accomplish removal of the inner receiver, click here: P-11/P-40 and P-32/P-3AT Disassembly

thanks thats perfect