There are a few different ways to upgrade from Windows 10 1803 to 20H2:
1. Use Windows Update
Windows Update should automatically download and install the 20H2 update for you. To check for updates, open Settings, then go to Update & Security > Windows Update. Click Check for updates, and then install any available updates.
2. Use the Media Creation Tool
If you're not seeing the 20H2 update in Windows Update, you can try using the Media Creation Tool. This tool allows you to create a bootable USB drive or ISO file with the 20H2 update, which you can then use to upgrade your computer.
3. Use an ISO file
If you prefer, you can also download a standalone ISO file for the 20H2 update. This can be helpful if you need to upgrade multiple computers, or if you want to create a backup in case you need to reinstall the update later.
4. Use the Upgrade Assistant
If you're having trouble with any of the other methods, you can try using the Upgrade Assistant. This tool will walk you through the process of upgrading to 20H2, and can help resolve any problems that you might be having.