@toril, is the reason for the change just because support for Windows 10 will end next year or do you really need to update/upgrade your computer?
If you are happy with your current computer and are using Windows 10 you should have a message on your Windows update page advising whether your computer is compatible for upgrading to Windows 11. If it is compatible then all you need to do is authorize the upgrade and Windows 11 will be installed.
ETA: In regard to the computers being offered there are some that are good (and oh so tempting) but I strongly advise staying away from any being offered with only 4GB of RAM.
What is good for the goose today will also be good for the gander tomorrow.