Well an easy way to do it would be to open the areo.msstyle with restorator and grab the image folder and drag it to the desktop and then open the folder and edit the relevant images, they are pretty easy to spot they are brightly coloured bars.
Once you have made your edits then change your theme to basic and then log off and log on again, then open the areo.msstyle again and you can either add just the images you edited by dropping them on the image folder or scroll down through the images until you find the image and drop it on the number that corresponds to the particular image.
Then save it and select your Areo theme again.