You need to purchase 2 "3-way" switches. Dont let that name confuse you. thats what you need if you want to turn the same light on/off at two different locations. However. you also need 3 wires (all of them insulated), AND a ground wire (this one doesn't have to be insulated) going between the two switches. This wire is commonly "12-3 with ground" and also passes through the light mount. Passing the wire through the light mount box is NOT requrired, but is commonly done. Anyway, its not just as simple as mounting two new switches. Follow the diagram in or on the 3-way switch package.