If you are working with a commercial printing service to print your publication, it's a good idea to go over any color changes you want with someone from the service.
Change to another spot color
Select the color you want.
Click More Colors, and then select the color you want.
Change from two spot colors to one spot color
Note When you switch from two spot colors to one spot color, objects that were filled with spot color 2 are changed to tints of black.