I suspect that you are raising this because the antennas on the Belkin aren't the standard removable type. To remove these you will have to open the case (carefully or you could tear an antenna cable inside).
Some antenna designs have a 'pigtail' screened lead which is soldered onto the circuit board, others may have that lead simply plugged into the board. Remove the lead from the circuit board (first noting which part the of the board the screening of the lead connects to).
The antenna may then be removed from the casing. If you leave the antennas in place, create a new entry point for your new antenna cable (drill the case or burn into it with solder iron and tidy up later with a file). Connect the new antenna to the appropriate part of the circuit board.