You're attempting to change the WordPress address and/or Site URL, however the values are unable to be edited as they are disabled / grayed out.
This occurs when the values are overridden within the wp-config.php file with a hard-coded value. Use FTP or the Plesk File Manager to navigate to your WordPress site's files and open up wp-config.php. Look for an option that looks like the following and either comment the lines out (put a # at the start of each line) or remove them:
My WordPress Address and Site Address URLs are disabled in General Settings