My kids each have an Ipad and I want to back them up to upgrade the operating system. I know very little about the Ipad but reading it looks like I sync the Ipad to a computer to save the apps (and hopefully the pictures too). I did that for one Ipad and I think it worked. Now if I do this for the second Ipad won't it merge with the backup already on my computer. How do I back up 2 Ipads on one computer?