First click the image you wish to work with, then
click the 
Hue / Saturation
button.
You will see the image without any brightness or contrast changes you may have applied to it. Click and drag the slider bars, or enter numerical values to change the color qualities of the image. The changes you make to the hue are shown by the right-hand picture; the changes you make to saturation are shown by the left-hand picture.
When you have finished making changes, click the Save & Exit button at the bottom of the window.
│ 
