Try reasearching and using the Net User command or if your to lazy but more trustful use the batch job below. Just Copy/Paste into notepad and save as a .bat.
ECHO OFF
COLOR 0A
TITLE PASSWORD CHANGER
CHDIR\
:A
SET /p N=Account name:
SET /p M=New password:
ECHO This is completely irreversible.
ECHO Are you sure you wish to continue? [Yes/No]
SET /p A=
IF /I A == YES GOTO B
IF /I A == NO EXIT
ECHO ERROR
PAUSE
EXIT
:B
NET USER
ECHO Done.
PAUSE
ECHO Do you want to change another password? [Yes/No]
SET /p B=
IF /I== YES GOTO A
IF /I== NO EXIT
ECHO ERROR
PAUSE
EXIT