colour image into black and white

[fishswim43]

I would like to turn a colour image into a black and white. I have tried this by going to image > Adjustment and Threshold but I am not sure how to turn certain white bits black.

[crickyE]

just hit ctrl and ''u'' at the same time and lower the saturation and mess about with the brightness to the right adjustment you want it.

im using pixbuilder pro not photoshop so the ctrl + u combination might be different on photoshop?