I’m a bit confused about where your confusion is.
If you want to remove a site in Matomo, you can go to the admin page , then select Websites -> Manage and then simply click on the delete icon for every site you want to delete.
It would be great if you could expand on where you were confused (ideally with screenshots) so that this can be improved in the future.
The All Websites tab doesn’t allow you to manage your websites. It doesn’t allow you to change the settings of websites, doesn’t show you the siteIDs and doesn’t allow you to delete websites. The only exception is the
Add a new website link which is just a shortcut to the admin page.
Instead, its purpose it to show you the reports.
The website management settings are in the admin aread where you can find all other settings and next to related things like excluded IP addresses, etc. and website-related settings.