James on "Error 500"

I have recently updated my wordpress site to the latest version of wordpress.
Now, both the website itself (www.sonitron.com.au) and the admin login page (www.sonitron.com.au/wp-login.php) show an error 500.
Is there any way that I can access the site and undo the update to get the site running again?
Thanks

Hi,

You need to contact your web hosting company.
Ask them to take a look at your error log to find out what is causing this issue.

If it's a theme or plugin. You can use FTP to access your server to remove it. Or ask your web hosting to help remove it.

If it's WordPress, you will need to re-install WordPress via FTP.
http://www.wpbeginner.com/wp-tutorials/how-to-manually-update-wordpress-using-ftp/

Ask your web hosting company for help, if you do not know how to use FTP.

Thank you

I have deleted all plugins and the theme, and have re-installed the previous version of wordpress (4.5.2) and I am still getting the error message.
Any suggestions?
Thanks

If you do not have access to your error logs, Denzel is correct, try and get a hold of your hosting company who can look at your error logs for you.