You need to provide more info... "fails every time" doesn't tell us much.
Try updating with iTunes.
The update starts to install showing that the download will take about 1 minute. Then switches to preparing update. When almost complete there is a pop up that says update failed.
Have tried resetting by holding the home and power buttons.
Try a different wifi connection... the one you're using might be blocking access to one of Apple's servers.
We have tried other Wifi and also have downloaded updates to this IPad previously. Please have had no issues with the other IPad using this Wifi
Make sure you have enough storage for the update, i.e. at least 3GB.
Retrieving data ...