Q: how do i download IOS 7.0 on my first generation IPAD?

So i have a first generation IPAD, and i havent used it in a long time as i use my mac more, but my stepdaughter is old enough to have it so i want to give it to her. but trying to download games/videos/tv series and more is proven to be very difficult as it is telling me i need IOS 7.0. its not telling me it needs a system update or even when i plug it into my mac it dosent say anything :/ hope someone can help.

Thanks in advance!.