Steps:-
Method 1:-
1) At the logon screen where it asks for password Press
"Ctrl + Alt + Del" 2-3 times .
2) A dialogue box will open with user account and password field
3)Enter "administrator" in user account field and leave the password field
Blank and Press ok
4)You will be then logged into administrator account and there you can
change password for any other account.
**This method will work only if administrator account is not locked**

Method 2 :-
**This method will work if that user account is already logged on and has
Administrative Privileges**
1)Goto run type "cmd" [without quotes] and click ok.
2)In cmd type the following command
net user accountname *
where account name is the Name of the user account.
3)Then it will ask for password type your desired password and hit enter ,it
will then ask for confirm password enter the password again and press enter.
4)You are done now ,You had sucessfully changed the password.