Yeah, as
oftheheavens tried, can you go thru iTunes? Might have more luck - might also encourage you to do a backup beforehand too!
(The install process via iTunes says it does one, but I always like to do my own beforehand, just in case. I do an 'Encrypt' version to my computer, and then 'Archive' it too - iTunes > Preferences > Devices > right-click backup > Archive. This puts a time and date on it and
should prevent it from getting overwritten by later backups)
OTA has been problematic for me in the past, too.