Change an image in Gimp with a gradient like a shiny button or sticker tab

Solution 1:

Brush > Colour Replacement

http://www.youtube.com/watch?v=Zm7BCw_E9wU

EDIT:
For GIMP -

Look at image title - if not RGB save it as .png or .gif
To change color wherever it is in entire image:
Select 'Color Tool' – (rectangular 3-color bar on top row)
Click on color to be changed
Select Edit and choose: Clear to eliminate color
Edit and fill with a) foreground color or b) background color

Solution 2:

In Photoshop use Image->Adjustments-> Hue/Saturation. For your image this would be the easiest way to change the color.

Solution 3:

You can use Colors>Hue-Saturation. Also Colorify works for some adjustments.

Solution 4:

i'll just post the colored version for you: