how to change the hand from left to right tell me (Hitman: Contracts)

Do you mean the hand? Change the control for the left hand, or have the Hitman himself hold the weapon in the other hand?
If the first, then invert the mouse in the control settings, if the second, then nothing.

If we are talking about changing the perspective "from left to right" and vice versa when firing a pistol, then in the aiming mode, press V on the keyboard (or L3 on the curling iron).