From the following Apple Support article: Resetting your keychain in Mac OS X
- Open Keychain Access, which is in the Utilities folder within the Applications folder.
- From the Keychain Access menu, choose Preferences.
- Click General, then click Reset My Default Keychain.
- Authenticate with your account login password.
- Quit Keychain Access.
- Restart your computer.
If applicable, continue with the following, from Mac OS X: Keychain Access asks for keychain "login" after changing login password
I don't remember my original (former) account password
In this case, you'll need to delete the keychain. Deleting a keychain also deletes all the password data saved in that keychain.
- In Keychain Access, choose Preferences from the Keychain Access menu.
- If available, click the Reset My Default Keychain button. This will remove the login keychain and create a new one with the password provided.
- If Reset My Default Keychain is not available, choose Keychain List from the Edit menu.
- Delete the "login" keychain.
The next time you log in to the account, you can save your current password in a keychain.