HT202650 how to reset login password

Question

I have an iMac (21.5-inch, Mid 2010) running OS 10.10.1 I was interrupted when changing our login password and can't remember new one I chose. The choice of use apple id to change password is greyed out. I am both admin and user.  How can I set a new log in, previously Utilites with software install could be used.

Answer 1

OS X 10.7 Lion, 10.8 Mountain Lion, 10.9 Mavericks and 10.10 Yosemite
Start the computer,then press and hold down command and R keys to start into recovery partition.
When you see the Apple logo, release the keys.
Wait until  OS X Utilities window shows up.
Move the mouse to the menubar at the top and click "Utilities", then select "Terminal"
from the drop down.
Terminal window will appear.
Type in   resetpassword   and press enter on the keyboard.
Leave the Terminal window open.
Reset Password Utility window will open with Macintosh HD selected.
Select the user account from the popup menu box under “Select user account”.
Enter a new password.
Reenter the new password for the user.
Enter a hint.
Click the "Save" button.
Click  in the menubar and select Restart.
Log in.
If Keychain dialog box appears, select “Create New Keychain”.