The current message provides incorrect instructions for most users with too users, as most users only have the two default groups for Confluence and should be disabling individual users instead.

Current message:
"You have more registered users than your license allows, either:
Contact sales@atlassian.com to purchase a larger license, or
remove the "Use Confluence" permission from some groups."

Example improved message:
"You have registered more users than your license allows. To disable unused users, [search for their username|../admin/users/browseusers.action] and remove their group memberships.

To upgrade your license for more users, check out our upgrade pricing and contact sales@atlassian.com."