The Modify an Account link in WHM can be used to update a cPanel account which you already created.
Domain - Used for updating the primary domain of this person's cPanel.
Theme - Controls the default theme for cPanel. We recommend X3.
Default Language - Controls the default language for this person's cPanel.
UserName - Used for updating the cPanel user name for this person's login. Resellers cannot update their own user name.
Max Email Accounts, Max Ftp Accounts, Max Mailing Lists, Max SubDomains, Max SQL Databases, Max Parked Domains, Max Addon Domains - Allows you to adjust these settings and override the package.