Below are guidelines for working in CMYK mode and adjusting the colours as required in Illustrator.
1. CMYK colour mode
It is best to compose your design in CMYK mode – but if you haven't done this, you will need to convert the colour mode before adjusting the colour values:
Select File > Document Color Mode > CMYK Color
Select Edit > Assign Profile
In Profile select "U.S. Sheetfed Coated v2" and confirm.
2. Converting all colours to CMYK
To ensure all of the colours used in your design are CMYK:
Select all objects
Select Edit > Edit Colours > Convert to CMYK
3. Adjusting colour values
You can now directly adjust the CMYK values used in your design.
When selecting colours and adjusting values, ensure you are using the CMYK sliders.