Hi I'm trying to update to 5.1 OTA on my 4s. I was going through a airport, and I started it there. It did some part, and I had to get on the plane. Now that I reached where I was going, I connected to wifi, and tried downloading.. Now it says "estimating time remaining" and crashes in a minute or two. What can I do? How can I update? >700 mb is a little big to download here.