Final answer:
To prevent a user from changing permissions for other users, the network administrator needs to remove the 'Modify' and potential 'Change Permissions' rights from that user for the specific folder.
Step-by-step explanation:
If a user is changing the rights to files in a folder for other users and the network administrator wants to prevent this, the administrator will need to adjust the permissions that the user has on that folder. Specifically, the administrator should remove the Modify permission, which allows users to add, delete, and change files, and may also need to revoke the Change Permissions right if the user has that specific ability. On systems like Windows, these permissions can be configured in the properties of the folder under the Security tab; for UNIX/Linux systems, this would involve changing the file permission with the 'chmod' command or adjusting group memberships or ACL (access control list) settings.