Very easy. ^^
Save the picture, once you save it, you go to your group, pass your arrow mouse around the icon till you see a white outline with a little pencil, click on it, there will appear your options to upload the picture, find the picture you saved, click it, let it upload, and once you do the adjustments of zooming to get it perfect and how you want it to fit, then click save, and done. ^^
Hope that helps.
Good luck! ^^
If it does not work, let me know. ^_^