There are a variety of reasons you might no longer want to be able to use a particular diagnosis in the EMR: it might have become a non-billable code, you might have found a code that fits your preferences better, or you might have manually created a diagnosis with incorrect information. When this happens you can disable the code without impacting patient orders and encounters that already list the code.
If you have a diagnostic code that you no longer want to have on your favorites list (i.e. you do not want to be prompted to diagnosis it when searching) you can disable it from the Admin > Manage > Diagnostic Codes management window. Bring up that management window, search for the diagnosis that you want removed, and click the diagnosis name.
The resulting editing window that pops up will have an option at the bottom to inactivate that code:
Once you've selected the Disabled value just click "Edit Diagnosis" and it will not longer appear as a prompt when diagnosing patients.