If you’re working with a Photoshop file that’s been created in a color mode other than CMYK, you can change the file’s color mode to CMYK by following these steps:

  1. Open your Photoshop file in the program.
  2. Select the document’s background layer by clicking on its thumbnail in the Layers panel and then clicking on the trashcan icon next to it. (If your document has more than one background layer, select the one you want to work with.)
  3. In the Layers panel, click on the “New Color Mode” button (it looks like a triangle with three arrows pointing down) and select “CMYK.”
  4. Click on the “OK” button to apply your new color mode to your document. ..