Update

See this for help with over the air updates. Get help with over-the-air iOS updates - Apple Support

If that does not work, then connect the phone to the computer with the latest version of iTunes and update that way. Update your iPhone, iPad, or iPod touch - Apple Support

Go to Settings > Storage and see if you have a previous download. If you do delete it and try again.

That is all it does, posts one word, Error?

I would say yes at this point.