You need to be an administrator to remove OS X Server.
When you remove the Server app, the services are turned off, but the service data remains in place until manually removed. For example, shared files and folders remain on the hard drive. Open Directory users remain on your Mac. Other services and service configuration files remain in place, but inactive.
To remove service data and service configuration data, you need to remove the Server support folder. To remove shared files and folders, you put them in the Trash. To remove directory user accounts, you remove them from the Users pane before removing the Server app.
Removing Open Directory components is not supported. Open Directory remains configured and running even after the app is removed.
Sharing, Remote Login (ssh), and Remote Management (screen sharing) remain configured and running, and can be configured using System Preferences.
If you want to remove local network user accounts, delete them from the Users pane of the Server app.
Drag the Server app from the Applications folder to the Trash, then wait for the OS to detect the change.
Delete the following folder and files:
The Server support folder at /Library/Server
The preference files for Server: /Library/Preferences/com.apple.serverd.plist and /Library/Preferences/com.apple.servermgrd.plist
To reveal the support folder and preference files, choose Go > Go to Folder in the Finder, enter the file locations above, then drag the folder or files to the trash (or delete the folder and its contents using Terminal).