I have also forgotten my adminstrators password!
Apple menu > Logout Guest
OS X 10.7 Lion /10.8 MountainLion
Follow the instructions in the first and the third boxes.
Well, that was easy. Guest user logged out. Thank you! Now to reset administrator passwaord....
Sorry for my ignorance, but I don't think the user password is the same as the administrator password.
Also, what is a keychain password?
Click in the box under "Select the user account".
Select your administrator account.
A user can be an "Administrator".
OS X keeps all passwords in an application/utility called Keychain Access
for easy management of various passwords.
Retrieving data ...