Hi,
You could configure WordPress in a separate directory. If you're installing WordPress manually, just create a new directory in public_html and upload the WordPress files there. If you're using the automatic installer (or "Softaculous"), it should ask you where you want to install WordPress.
When you're ready to switch it over, you would need to change the Site URL configured within WordPress, by logging into WordPress and changing "WordPress Address (URL)"/"Site Address (URL)" within the Settings > General section. Then, you can move your old site's files out of the way (using either FTP or cPanel File Manager), and then move the files within your public_html/wordpress directory into the public_html directory.
Thank you,