A WordPress Administrator is one of six predefined roles assigned to site owners upon installation of WordPress. A site owner with WordPress Administrator status has comprehensive control and management capabilities over what users can or cannot do within their site.
What Can a WordPress Administrator Do?
The WordPress Administrator is the only user role that can upgrade a site blog. They can also change themes and edit core files by using the built-in theme editor. Moreover, they can add and remove other Administrator users. When assigning this role to a user, remember that they can delete content.
So, make sure to give Administrator roles only to trusted people. The role allows complete control over the entire site. Administrators can delete pages and posts, activate and install plugins, etc. If they are not using multisite, they can even delete everything!