There are many ways you will read about to convert a colour digital image to Black and White, there is the lazy way of just performing a de-saturation or just selecting Mode and Grey scale, I use a method called the Lab technique, there are several steps to perform, but I feel that I have more control over the final image.

First step is to open up your colour image in Photoshop, open up the path dialog, Window > Paths

Convert the image to Lab Color, Menu > Image > Lab Color

Now just select the lightness channel

Convert the image to Greyscale, Menu > Image > Greyscale

Convert the image to RGB Color, Menu > Image > RGB Color

Now we need to duplicate the layer, Layers > Duplicate

Choose Channels on the Paths dialog and select Multiply

Next Change the Opacity to 50%

Now create a new adjustment layer for channels, Layer > New Adjustment Layer > Channel Mixer

On the dialog check the Monochrome box and adjust the color sliders until you are happy with the image

Now you can do any other adjustments and save with a new name