If you are using windows 10 and accidentally or due to some other reason you are using Microsoft account to log in to your Windows, and want to revert back to a local account, then here is the solution.
Converting Your Microsoft Account Back to a Local User
Step 1: In the search panel search for accounts and select “Change your account picture or profile settings” as seen in the screenshot below.
Step 2: When the Account Settings menu opens you’ll see your currently activated email address. Below that you’ll find a link, labeled “Sign in with a local account instead”. Click on that link.
Step 3: A screen will open, asking for your current password which is associated with your Microsoft account. Enter the password and click “Next”.
Step 4: Enter a new local username and password, click “Next”.
Step 5: Click “Sign out and finish” and you are done. The last page is just a confirmation and a reminder that this will only change the local login and not your Microsoft account.