Replace Current Password of your PC without knowing it

First of all goto START menu and click on RUN then type LUSRMGR.MSC and press OK button
Then double click on USERS, Right click the user which you want to change the password.
Then click on SET PASSWORD.
Type the same password in both boxes.
Note-There is no need to enter current password

Now go to CONTROL PANEL and open USER ACCOUNTS select the user name and remove your password if u want.