With the engine at idle speed, depress the brake down firm, very firm and it should shift easily. Also be sure that it isn't in 4 WD, and if it is shift that to 2WD and try again.
It shouldn't be that hard to shift unless something is damaged. If the above advice doesn't work, as you SLOWLY move the selector from reverse, lightly tap the accelerator pedal with slight pressure on the gear shift selector and then release the accelerator pedal. Be sure to not advance the throttle much, only very slightly.
Hope these work for you, and please report back with your results.