Follow the install instruction that appears on your install wizard.
Once you're done with the installation process, you need to update your company file:
Open your new QuickBooks 2021, then select Open your restore company file.
Make sure to open the correct company file.
I also suggest contacting our Quickbooks Desktop support team to stay with you in doing the process. This will help you upgrade your QuickBooks seamlessly and you can also ask questions with the support as you go through the process.
Let me know if you need additional information in upgrading your QuickBooks version. I'll be happy to help you further. Stay safe and have a good day.