Hello,
Please do make sure you run the PC health check app to ensure it is indeed meeting all requirements: https://support.microsoft.com/en-us/windows/how-to-use-the-pc-health-check-app-9c8abd9b-03ba-4e67-81ef-36f37caa7844
If so, You can go to the following website: https://www.microsoft.com/software-download/windows11
Download and run the Installation Assistant, and choose the upgrade option from there.