Please note: this question assumes that you know your current password and would like to change it after logging in. If you have forgotten your password completely and need to reset it, take a look at this FAQ page.
After logging in, you will simply need to click 'My Account' at the top-right corner:
In the middle of the page in the 'My Security' section, you will see an option to edit your Password or Security Questions:
Changing Your Password
Clicking the edit button next to password will prompt you to enter your old password once and your new password twice:
You will then be prompted to answer your security question to confirm your identity:
After entering your answers and clicking submit, your new password will be active. Please remember this password for your next log in and keep it secure.
Changing Your Security Questions
Clicking the edit button next to security question will prompt you to select your new questions and enter your new answers:
You will then be prompted to enter your password to confirm your identity:
For further security purposes, you will need to retrieve an e-mail code to validate your identity:
Note that if you do not receive this e-mail within several minutes, you should check your Spam or Junk folder. Once you retrieve and enter this code, your new security questions and answers will be active.