It is a good security practice to change your password periodically, and to use passwords that are not easy to guess by someone who knows you. Whenever you login, the Homepage page tells you when was the last time you logged in, and when was the last time that you changed your password.
To change your password you can:
click on change password in the Homepage page
click on Preferences on the menu, click on General and click on the Change button in the Password field