1. Go to Extensions

2. In the extension click Edit

3. Scroll down to the Greetings section

4. Press "Upload or Record" button

5. You can choose to upload an existing file, or "Record by Computer"

6. Click "Record"

7. Click "Start" and then press the red button to begin recording

8. Click "Review" button to review the recording

9. Click "Save" button to save it.