The above 3 way switch wiring diagram shows a typical 3 way switch installation. The top 3 way diagram shows the light switches installed and wired to control one light from two locations.
In electrical renovation you may want to change from a 3 way switch control to a single switch control. The botton wiring diagram shows you how to abandon the first 3 way switch and change to a single light switch control. Basicaly, all you have to do is tie the blacks together in the first box and abandon the red traveler wire. Then in box 2 use the black with a single pole light switch and again, abandon the red traveler wire.