You should remove an accessory module from the main Station only if the module is not in use anymore or before replacing it.
Removing a module is useless when:
Having disconnection issues;
Having measurements issues
Having trouble receiving notifications.
1. Go to Settings > Manage my Home
2. Select the room where the module is and click on the module
3. On the module page, click on the 3 dots on the top-right corner and select Delete
4. Follow the instructions of the application (e.g. plug the Main module, touch the top until the LED flashes...) in order to remove the accessory