Howdy venus120,
Thanks for following up with this information.
While you may be able to wait to try with a different Wi-Fi network, you may need to use a computer at times to install the update. This could be related to the network speeds, size of the download, as well as other factors so using a computer will help to remove those factors from preventing the update.
If you prefer to use a computer as opposed to waiting, you may be able to locate an Apple Store or Apple Authorized Service Provider if a family member or friend doesn't have a computer to use. If you'd like assistance with locating what's nearby, use the following link to select your country and locate service options: Apple - Find Locations - Location Selector
We hope that's able to help.
Have a great day.