The update to 4.5.x has to be done manually from the version you are running, please refer to my replies in this thread: <a href="https://kriesi.at/support/topic/enfold-4-5-theme-update-update-failed-download-failed-a-valid-url-was-not-pro/#post-1021541" rel="noopener" target="_blank" rel="nofollow">https://kriesi.at/support/topic/enfold-4-5-theme-update-update-failed-download-failed-a-valid-url-was-not-pro/#post-1021541</a>

You can either update manually via FTP: <a href="https://kriesi.at/documentation/enfold/how-to-install-enfold-theme/#theme-update" title="https://kriesi.at/documentation/enfold/how-to-install-enfold-theme/#theme-update" rel="nofollow">https://kriesi.at/documentation/enfold/how-to-install-enfold-theme/#theme-update</a>, or use a plugin to upload the theme zip file: <a href="https://wordpress.org/plugins/update-theme-and-plugins-from-zip-file/" rel="noopener" target="_blank" rel="nofollow">https://wordpress.org/plugins/update-theme-and-plugins-from-zip-file/</a>

If that doesn't work then please try to delete the whole theme folder, then replace it with the new version. Make sure that you have backups of the site before starting updating.

After you have updated then try to activate the Classic Editor in the main page of the theme options.

Also please read this after you have updated: <a href="https://kriesi.at/documentation/enfold/theme-registration/">https://kriesi.at/documentation/enfold/theme-registration/</a>