Error .. Popup Builder plugin requires PHP version >= 5.3.3 version required.

Your plugin requires a greater version of PHP, which obviously your server doesn’t support.
To access your website again you need to delete that plugin from the server. Go to your cPanel and open File Manager then navigate to your WordPress root folder > wp-content > plugins inside you will see a folder of popup builder select it and delete it, this way you will have access to your website.

As for the PHP version, try contacting your hosting company and ask them to update it, since it is not recommended to use old versions because of the security issues they have and they are no longer supported.