Thanks for your help. Internetse provide me with Wordpress to edit my website. I have asked them how I can upload the text files and they said send them to us, which I’ve now done.
I have installed the WP File Manager plug in, which from its description should allow me to upload files, but I can find the webroot directory for my website. It seems very strange that wouldn’t be accessible, but the plug in is not that intuitive for doing that and I haven’t found better instructions on line yet.