The Windows 10 username you choose when you first use Windows 10 can be changed at any time. If this username is tied to a Microsoft account, the procedure is as follows: log in to Windows 10 with your Microsoft account and go to account.microsoft.com/profile/ in your browser.
On private computers that are only used by one user, it really makes no sense to have to enter a password every time you startup. Good thing Windows 10 offers a relatively well-hidden feature for this. Use the Windows+R hotkey to open the Run window, type “netplwiz” and confirm with entering. In the User Accounts window that now opens, bring the Users tab to the front, uncheck the You must enter a password and username to use the computer before you can use the computer option, and click OK.
Even if there are some advantages to logging in with a Microsoft account, such as using OneDrive, many users still prefer to work with a local account. However, Microsoft is not one to give up easily and points out at every login that it would be much better to use a Microsoft account.