hi mate! you can do it in 2 pretty simple ways.
1. if you created the kits with vectors, you can simply take all vectors from the 07 front and resize it to the 08 front's size and drag the objects from the 07 template to the 08.
2. if you have made it another way, with pen tool etc, i'd suggest you to merge the kit and then copy the front and paste it into the fifa 08 texture. then transform it (ctrl+T) into the 08 size. ok,now you have a merged and blurry front, but this is just made as a template, so now you create the design again, having the merged front as help so you know where to drag your new lines
thats how i would do,maybe someone else have other options!