Hi Andrew,
Thanks for reaching out although I’m sorry to hear your site is down. If Total Upkeep is the culprit you can deactivate the plugin from your web host File Manager or via FTP. You’d need to access your file system and find and rename the Total Upkeep plugin to regain access to your site.
You can find your WordPress plugins folder in a /wp-content/plugins section of your website file structure.
I hope this helps Andrew.