Update any plugins that need it, before you upgrade WordPress.
I just mindlessly upgraded to WordPress 4.3 and got the white screen of death. Called that because you get no errors – simply no site. I remembered too late that I had a plugin that needed updated. Just FTP or CPanel to that folder in wp-content/plugins and temporarily rename or delete the plugin (or rename the entire plugins folder to plugins-old. Reload your site. If it shows, update the plugin, or keep the offending plugin deactivated. And stop rushing around like you’re putting out fires. Stop and think before you act. (I’m talking to myself)