The environment variable USERNAME is defined in the registry key HKEY_CURRENT_USER\Volatile Environment.

Note however that as the keyname implies, the variables in this key are volatile, meaning that while the user can change them, they will not retain their new values and will be overwritten by the system with derived values (sort of like registry RAM). The username environment variable is one of the few variables that cannot be set, or even if they are, they will not “stick”, just like how setting a variable in a console session is lost when you open a new one.

It should update the variable with the new user name. Have you tried logging out and back in or rebooting the system?

Where/how did you change the user name, the User Accounts Control Panel applet? The User Accounts applet only changes the user’s name, not the actual username. Use lusrmgr.msc to modify the user name by clicking it, pressing F2 and changing it (then log out/in or reboot).

If that does not work, then search the registry for the old/original user name and change it there(s?). Check the following keys:

HKLM\SOFTWARE\Microsoft\Windows NT\CurrentVersion\ProfileList
HKLM\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon\SpecialAccounts\UserList

If you want to change the windows USERNAME environment variable string, you can do this in the Advanced User Accounts Control Panel.

Open it by running netplwiz ("C:\Windows\System32\Netplwiz.exe", network places wizard). Then select the name you want to change and click on the Properties button. Now you get the properties of the selected user account: you can change the User name (, Full name & Description) here. You'll (just) need administrator rights to do this.

Log out and log on, open a command prompt and try to output the value for %USERNAME%. You'll notice it has been changed according to your modification.

One thing you can do is change the NAME of the computer to something sensible to you. This helps when creating new user accounts.

What I found in looking is that this is a long standing bug https://answers.microsoft.com/en-us/windows/forum/all/changing-user-folder-name-windows10/77a01554-1002-48f4-91c8-f438862df771

So one thing you can do is make a new account of your choice.

Is there an environment variable that by points to

C:\Users\%USERNAME%\AppData\Temp

No

Or maybe

C:\Users\%USERNAME%\AppData\local\Temp

The default value for %TEMP% and %TMP% is C:\Users\{username}\AppData\Local\Temp

Windows 7 Environment variables

Variable                   Windows Vista/7
%ALLUSERSPROFILE% 
(%PROGRAMDATA%)            C:\ProgramData
%APPDATA%                  C:\Users\{username}\AppData\Roaming
%COMPUTERNAME%             {computername}
%COMMONPROGRAMFILES%       C:\Program Files\Common Files
%COMMONPROGRAMFILES(x86)%  C:\Program Files (x86)\Common Files
%COMSPEC%                  C:\Windows\System32\cmd.exe
%HOMEDRIVE%                C:
%HOMEPATH%                 \Users\{username}
%LOCALAPPDATA%             C:\Users\{username}\AppData\Local
%LOGONSERVER%              \\{domain_logon_server}
%PATH%                     C:\Windows\system32;C:\Windows;C:\Windows\System32\Wbem;{plus program paths}
%PATHEXT%                  .com;.exe;.bat;.cmd;.vbs;.vbe;.js;.jse;.wsf;.wsh;.msc
%PROGRAMFILES%             C:\Program Files
%PROGRAMFILES(X86)%        C:\Program Files (x86) (only in 64-bit version)
%PROMPT%                   Code for current command prompt format. Code is usually $P$G
%SystemDrive%              C:
%SystemRoot%               C:\Windows
%TEMP% and %TMP%           C:\Users\{username}\AppData\Local\Temp
%USERDOMAIN%               {userdomain}
%USERNAME%                 {username}
%USERPROFILE%              C:\Users\{username}
%WINDIR%                   C:\Windows
%PUBLIC%                   C:\Users\Public
%PROGRAMDATA%              C:\ProgramData
%PSModulePath%             %SystemRoot%\system32\WindowsPowerShell\v1.0\Modules\

Source Windows 7 Environment variables

You can use the username variable: %USERNAME%

Here is another batch file solution with code similar to code written by Martin Prikryl with three enhancements.

1. %USERPROFILE% is used instead of C:\Users\%username% which makes this batch file solution work also on Windows XP and on machines on which the user's profile directory is not on drive C: or in a different directory than C:\Users which is of course possible too.

2. %SystemRoot%\System32\ftp.exe is used in the batch file instead of just ftp to make this batch file work also if by chance there is an ftp.* file with a file extension listed in environment variable PATHEXT in current directory or any other directory in environment variable PATH and not being the ftp executable in Windows system directory.

3. The ISO file name is renamed before upload with including a random decimal number between 0 and 32767 as asked for with a comment.

The command lines of enhanced batch file:

:RandomIsoName
set "RandomName=mini_%RANDOM%.iso"
if exist "%USERPROFILE%\Desktop\ISO's\%RandomName%" goto RandomIsoName
ren "%USERPROFILE%\Desktop\ISO's\mini.iso" "%RandomName%"

(
echo open hostname
echo username
echo password
echo cd \wwwhome\Logs\
echo put "%USERPROFILE%\Desktop\ISO's\%RandomName%"
echo bye
)>ftp.txt
%SystemRoot%\System32\ftp.exe -s:ftp.txt