Log in to your computer with your old password or your temp one given to you by IT or your supervisor/manager.
1) Once you see your desktop, press ctrl + alt + delete on your keyboard
2) Choose Change a password

3) You will be prompted to enter your old password or the Temp one given to you, and then a new one.
***NOTE*** You can not use any part of your old password from the last 5 that you have used.