Your users are unable to uninstall the UEMS Agent from Add/Remove Programs, as there is no provision available to do the same.
You may encounter this problem if, you have enabled the "Disable Uninstallation Option in Control" check box under Admin -> "SoM Settings" -> "Agent Settings" while deploying agents to computers.
Revoke User Permissions to Add/Remove Programs
If you want to allow your users to uninstall agent from client machines,
The update will get reflected during the subsequent communication between the Agent and the Server. And the users will be able to see options to add or remove under the Add/Remove Programs section.
Uninstall from Client Machines individually
Using this method, you can manually uninstall the agents from the desired client computers.