Adjusting colours with Gimp

Open the ‘Gimp’

Open the file ‘neil here.xcf’
In the ‘Layers Window’ select the layer that you would like to
change the colour of.

Use the Rectangle select tool to select the image you want to
use.

Go to ‘Colours/Brightness-Contrast’.

Use the sliders to change how bright the image is.
Contrast means how much difference there is between the bright and the dark colours.

When you are happy with the change, press ‘Enter’ on the keyboard.
Go to ‘colours/hue-saturation’ to change what colour the image
is.

Changing the hue will change what the colour is.
Changing the saturation will change how strong the colour is.