I can not download iOS7.1 to my mum's ipad when it says Install Now, I tap it, Agree to terms and conditions, and then it come up with Software Update is not available at this time. Try again later.I have tried and its still not allowing me to update.

Hello, Owen.

Thank you for visiting Apple Support Communities.

Here is the best troubleshooting article to go through when experiencing issues updating your iOS device over-the-air.

Resolve issues with an over-the-air iOS update

http://support.apple.com/kb/TS4431

You can also update this iPad via iTunes on a computer as an alternative.

Update your device using iTunes

If you can’t update wirelessly, or if you want to update with iTunes, follow these steps:

1. If you use your device's Personal Hotspot for your computer's Internet connection, update your device wirelessly or connect your computer to another network.
2. Install the latest version of iTunes on your computer.
3. Plug in your device to your computer.
4. In iTunes, select your device.
5. In the Summary pane, click Check for Update.
6. Click Download and Update.

If you see an error message while updating your device, you can learn how to resolve iOS update errors in iTunes.

Update your iPhone, iPad, or iPod touch

http://support.apple.com/kb/HT4623

Cheers,

Jason H.

check the available space on the device. It may be too full to perform the update.