Usually when you open your Outlook desktop client after you've changed your password, a box will pop up asking for your username and password. You can enter your new password, and check the box in front of Remember my credentials. That way, you won't have to enter your username and password every time you open the Outlook client on your desktop.
Sometimes, however, your Outlook won't ask you to input your new password. You can force your email to do so.
1. Click on File at the top left of your Outlook screen.
2. Click on the Account Settings button to bring up the menu, and press Account Settings from that menu.
3. Double-click on the email account name.
4. Click on the More Settings button.
5. Under the Security tab, click on the box in front of the Always prompt for logon credentials field and press the Apply button and then the OK button.
6. Close all the windows, and then close Outlook. Re-open Outlook.
7. Enter your username and new password and make sure to check the box in front of the Remember my credentials field. If you still keep getting prompted for your password each time you log in, go through the steps above again, except un-check the box in front of the Always prompt for logon credentials field.