There are two kinds of methods: destructive and non-destructive.
Destructive methods doesn’t allow to re-adjust after conversion. The only option is to undo the conversion and start again.
Non-destructive methods use layers so that the changes are stored in layers and original photos are unchanged
Converting to greyscale discards all the color information in the photo.
Image -> Mode -> Grayscale
2. Image adjustments to black and white
Image -> Adjustments -> Black & White
3. Lab Color
- Image -> Mode -> Lab Color
- Channels window -> Lightness channel
- Image -> Mode -> Grayscale
4. Hue/Saturation Tool – working on layer
The result is the same as method 1.
- Layer -> New Adjustment Layer -> Hue/Saturation
- Saturation = -100