Remove the firmware upgrade notification on Android phone

It may be different for various brands of the phones, however this is one kind of tricks you may try.

First try to change the upgrade option to Download Update Manually, usually from the Settings|System Updates option.

If after that the notification still shows up, we can clear the data and cache of the Update App to remove the notification from the notification bar. To do that:

1. Go to Settings
2. Select Apps & notifications
3. Select App info
4. Click on the menu and choose Show system
5. Find the update app (e.g. FOTAService)
6. Click on the Storage item of the app
7. Clear both data and cache
8. The notification is gone from the notification bar