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.
If you are not automatically logged in, click on the circle icon at the top right and enter the email address associated with your Microsoft account, followed by the password. On the next page, click on the current name in the top left corner to open the Your details page. Here click on the Edit Name link, rewrite the first and last name, enter the captcha code you receive, which is case-insensitive, and click Save to approve.
If you use Windows 10 with a local account, it’s even faster. Open the classic Control Panel, for example, by clicking the Start button, typing Control Panel, and clicking the result. With the Category view active, click on the User Accounts category and select User Accounts again. If another view is active, just click on User Accounts. Then select the Change name for the account link, type in the name you want, and click the Change name button to approve. As an administrator, you can also edit the accounts of other installed users in the User Accounts area. To do this, click on the Manage another account link and select the desired account.