well u all knw how to crack passward in os.
but let us tell u the easiest method

How to Change Window 7 Password without KnowingCurrent Password



METHOD 1: 

1.Go to Control Panel and click on the Administrative Tools. 

2.Under this section double click
on Computer Management. Select System Tools from right window pane. 

3.Under this, just double click
on Local Users and Groups and then on Users 

4.Now you will see all the login
accounts of your computer.

5.Right click on any the account
whose password you want to
change and then click on Set Password. 

6.A warning message will popup on your screen just click
on Proceed button. 

7.Now enter your New Password and click on OK button. 

That’s it! your windows 7
password is changed without
knowing current password.

Note: The only limitation of this
method is that your current
account should have Administrative privileges. 



METHOD 2: 

If you love to be work on
Command Line then this
method is for you.

1.Open command prompt Type CMD in start, right click on it and select Run as Administrative 

2.In the CMD window type the
following command and
hit Enter "net user Account Name Your
New Password" without quotes 

3.In this command replace
Account Name by the account
name (Account Name is case
sensitive) whose password you want to change and
replace Your New Password
by the password that you
want to set. 

Now if everything goes alright
you will see “The command
completed successfully” on
your screen, 

4.now
type exit command and hit Enter This will reset your current
windows password. 

U can change administrator password by this through guest account 

enjyy