Refer to the Documentation. We work hard to ensure this is as detailed as possible, and covers as many questions / how-to’s.
Clear any browser caching by force refreshing the screen in question
Clear any server caching in the WordPress Administration interface
If technically able to, view your web browser’s console/log, performing the steps/tasks that you were unable to perform and including any error messages displayed.
If technically able to, add the following to your wp-config.php file, performing the steps/tasks that you were unable to perform and including a copy of the resulting wp-content/debug.log file: