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Basically you could opt for the desaturate option from Image > Adjustments > Desaturate or the shortcut Shift + Ctrl + U
If you want a more advanced technique you could use the Channel Mixer from Image > Adjustments > Channel Mixer and on the bottom left click on Monochrome and adjust the sliders until you get a desired result.
You could also go to Image > Adjustments > Hue/Saturation and make the Saturation=(-100)
There's also Image> Adjustments > Black/White
You could also Image> Adjustments > Gradient Map and assign a black and white map
