New
#1
You can't reliably rename it - you need to add a new user account.
If you add a local account it will create the folder name you give it. See option 3 here https://www.tenforums.com/tutorials/...a.html#option3
Make it an administrator account. Account Type - Change in Windows 10
You can then sign on to it and link it to a Microsoft account if you wish. Microsoft Account - Switch to in Windows 10. If you create it as a Microsoft Accounts straight off it will give that folder a odd truncated name.
Once you are happy with new account you can move all your documents etc from old account to C:\Users\Public\Documents and delete the old account. Then move them from C:\Users\Public\Documents to wherever you want them in your new account.