With the lamp still selected, you can open the Object Data tab in the properties window in Blender to see all options related to lights. At the top, you can change your light type and set values for color and energy.
The first option will set the color that your light will emit, and the second, specifies how intense your light will be, as shown:
The Object Data tab changes based on context. For instance, when you select a lamp, it will display options for that object type. If you choose a 3D model, it will show options related to that object.
