how can i reset my administrator password if i forgot the password?

1. Did you try using your Apple ID to reset the password?
2. Did you enable FileVault?

If you get nowhere:

Changing or resetting an account password (Lion):

http://support.apple.com/kb/HT1274

Scroll down to Resetting the original administrator account password. Try the procedure under reset your user password with your Apple ID.

If that does not work for whatever reason you can also use the following technique:

1. Restart your Mac while holding down the ⌘ and R keys at the same time until you see the Mac OS X Utilities screen.
2. From the menu bar at the top, select Utilities > Terminal.
3. In the Terminal window type resetpassword and press Enter. A window will open behind Terminal that looks like this

1. Select your startup volume ("Macintosh HD" in the above screenshot), choose your user account from the dropdown selection, enter a new password, complete the password hint field, and click Save.
2. You may then see a confirmation dialog explaining how this change affects Keychain Access and what to do about it. Remember it or write it down, then click OK.
3. Quit Reset Password
4. Quit Terminal
5. Quit OS X Utilities and restart your Mac.

Password is case sensitive.

Reset Password

Follow the instructions in beige and green boxes.

http://pondini.org/OSX/Password.html

Note

Mac OS X: Keychain Access asks for keychain "login" after changing login password

http://support.apple.com/kb/HT1631