Updated. Extending Range of a microstrip antenna with a SMA 2.4GHz Omni Direction 20db wifi antenna
Don't bother removing the antenna.  What you should do is remove the matching network, and connect the cable directly to the output of the module.  If you follow the antenna trace, there are three surface mount footprints that it passes by - one in series, and two in parallel to GND.  Remove these three components.  Actually, there might only be one in series; I can't really tell from the pictures.  Then connect the center conductor of the coax to the trace coming out of the module and the shield to GND.  You need to make the leads hanging off the end of the cable as short as possible for the best performance.  You should also find a way to secure the cable so that it doesn't get yanked, damaging the connections.