Can’t upgrade wordpress and no .maintenance file to delete

I am trying to update my website to WordPress 4.9. https://www.bateson4business.com

The install starts unpacking, then hangs on “Could not copy file:…”

Searching the Internet says to delete the .maintenance file from the root directory but *there is no* .maintenance file anywhere on my site.

1) How can this be?
2) How can I upgrade to WordPress 4.9?

Many thanks

Finn

The page I need help with: [log in to see the link]