you can change administrators password without knowing old password
right click on my computer....
(1)click on "manage",
(2)new window of "Computer Management" will get open.,
(3)now on the left side of the window...click on "Local Users and Groups",
(4)now on the right side double click on "users", then
(5)right click on "Administrator".then
(6)click on "set password"...
(7)then just change it....n then njoy..... u can also change it by login with any account other then Admin account.