When you press the gearchange pedal down you should be able to feel the spring pushing back against your foot. If that pressure isn't there then you need to reset it as per the manual.
http://www.ferret-fv701.co.uk/manuals.htm
To go from forward to reverse with the vehicle stopped press your foot on the brake pedal this holds the vehicle in place and stops the box moving. With the vehicle stopped and in gear press down on the gearchange pedal down and at the same time as the pedal is going down move the forward / reverse lever in one swift movement either forward or back.
If you try changing from forward and reverse on a slope and don't press your foot on the brake pedal the vehicle can creep forward and you will not be able to change the direction off drive