Synopsis: Create a local administrator account, rename the user account, rename the user profile folder, and map the renamed folder to the user account in the registry.
Create a system restore point.
Create a new local admin account.
Log out and log in as the new admin account.
Run lusrmgr & rename the user account.
Rename the profile folder–> \Users\oldname to newname.
Map the renamed folder in the registry.
Regedit: Go to HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\ProfileList
There will be sub-keys with long names. Search for the ProfileImagePath value to find the one the corresponds with the old profile folder name. Edit that value to reflect the new folder name. You can find the SID using wmic useraccount get name,SID
Log out, and login as the renamed user. In some cases a reboot may be necessary. Test that everything is working properly.
Source: How to Rename User Profile Folder in Windows 10