I am trying to edit a picture that is mostly black with values CMYK - 75 68 67 90 and near and Total Ink value of 300. I am looking to bring the CMYK values of this down to CMYK 40 20 0 100 as recommended by my printer. How do I do that?
Your printer is lazy. n_n
The CMYK values depend on the design.
Leave thoose values alone. They are correct.
Black and white photography
If your image was intended to be black and white (grayscale) Ok. There is a chance it could work lowering the values, but to tell you the truth you could have a not neutralized black and white image. Thoose values will give you a slight cold black.
Edited some time after.
The CMYK total ink coverage depends on the color profile used. The 300% value you have is given by the CMYK profile Swop V2 for coated paper and it is correct.
If you need to print on an uncoated paper, yes it is too much and you should use the uncoated profile, which has lower total ink.
But the values, CMYK 40 20 0 100 are from an "old school", where printers where afraid of putting too much ink on a black and white page.
In CMYK mode go to curves (image > adjustment > curves, or Ctrl+M/cmd+M) select desired channel and click on the line. Then manually set "input" value in both boxes. So for cyan 40, 20 for magenta. Then go to layers tab, select "yellow" channel and mark it with "rectangular marquee tool". Fill it with white. You can also duplicate the yellow channel, fill it with white and then delete the previous one.