Change your password to something memorable so you never get locked out of your account. Navigate to My preferences under your username in the top right corner of the screen. 

Scroll to the bottom of the View my profile page and select the Change Password button.

A screen will appear prompting you to enter your old password and new password.

When this is done select Change password. 

If you don't know your old password, reset your password. Read more about resetting your password here.