Network Setup message: "We recommend you change your siteurl..." how to remove www from si

Upgrading an existing single site WP to Multi site with plans to use sub domains and domain forwarding.

During the Network Setup phase, the following message is received:

"We recommend you change your siteurl to before enabling the network feature. It will still be possible to visit
your site using the www prefix with an address like but any links will not have the www prefix."

In Settings > General:
Wordpress address (URL):
Site Address (URL):

How do I follow the recommendation and change the site URL without bringing down the WP admin and more? WP is installed in the www folder according to CPanel File manager. That is where wp-content folder and wp-config.php are located. Does this fit the 'install WP in root' recommendation i've read in forum posts?

What is the WPMU DEV recommended solution for the message encountered and for best functionality of the multi site as it grows? I have read on the forums that leaving www can cause problems in multi site going forward, and is more complex to work with. I would like to remove this without causing service disruption and to maximize multi site flexibility. Please keep in mind the Domain Forwarding preference, thanks in advance