Hello Ahmed, I'm Johrelle a fellow Windows/Microsoft user. I'm happy to assist you.
There seems to be some confusion between the display name and the actual username used for logging into the system.
You've successfully changed the display name that appears in the User folder and other areas of the Windows interface. This is purely cosmetic and doesn't affect the underlying username used for login.
Here's how to change the actual username. Open the Control Panel. Go to "User Accounts." Click "Manage another account." Select the account you want to change. Click "Change the account name." Enter the new username and click "Change Name."