Thanks. I got the version number from your model of Mac.
To reset the keychain password, you have to reset the admin password. You can reset the password ***** booting into Mac OS X Utilities screen. First go to System Preferences select iCloud. Click Sign Out button there and sign out. If asked to delete or keep stuffs, select Keep. If you only see Delete, then click Delete or OK. It is OK, you can reconnect to iCloud later (Ignore this step if already signed out there)
Then follow the steps below to reset the password.
Turn off your Mac.
Turn it back on and immediately hold down Command and R keys at same time for 10-20 seconds.
This will boot your Mac to "Mac OS X Utilities” menu.
Click on the“Utilities” menu in top bar and select “Terminal" (at the top of the screen)
Type (without space)--> resetpassword
Press return. This will bring Reset Password ***** Select the hard disk at top column,select the user account from the drop down under it, confirm the user account and then change password ***** Save. Then click on the Apple icon and select Shutdown.
Turn it back on. After restarting, if you get any message about Keychain then click Create NewKeychain. If that didn't work, then cancel that box.
Click on Finder icon on dock. Then in Finder, hold down Option key on your keyboard, click on Go menu at the top bar and select Library. This will open Library folder. Trash Keychain folder in there and restart your Mac. If it asks for keychain password, use the password ***** reset.
Please let me know if that didn't work, so we can continue troubleshooting.