BEFORE STARTING,
Please close your gimp.
If you don't already, download GIMP 2.8
First of, click here  to automatically download the themes.
Once finished, open it up, and press CTRL+A to Select them all, then
CTRL+C to Copy. Afterwards, go to COMPUTER > (C:) DRIVE > PROGRAM FILES
GIMP 2 > SHARE > THEMES and now press CTRL+V to Paste them all.

(Right Click > New tab to see it in a bigger version )

(If it somehow did not paste into there, if your using winrar, select all of them and extract
it to the desktop. Then you can drag&drop them all into the theme folder and see if it works)

NOW YOU WILL OPEN UP YOUR LOVELY GIMP. C:
You're almost done now. Just go to EDIT > PREFERENCES > THEMES
And just select the theme you want. (It'll show you a preview on how it looks)

Easy and simple right?
Hoped it help you guys.

Woot for two updates today! 8D