uncheck "Automatically Install Agent" on the collection in the Deployment Manager by right clicking the collection and click "Edit".
Once it is Unchecked "Install" and "Uninstall" options will be available.
If still not available
1. Click on the problem collection in InTrust Deployment Manager (there should be a computer list shown in the right panel)
2. Click 'Refresh' in the upper panel.
3. Wait until refresh is complete and check if install/uninstall agent buttons start working.
Please note that you should stay on the collection view during the refresh and not click anywhere else. To confirm the refresh is complete, check the lower left corner of the window - there should be 'Ready'.