1. Click on your name at the upper right corner of your browser window then select "Profile".
2. Click on Change Password and 3 new fields will show up.
3. Type your current password in Confirm Current Password field.
4. Enter your new password, which needs to be at least 8 characters now, in New Password and New Password Again fields.
5. Click on Submit and you have successfully changed your password!
If you don't know your password, you can reset it following instruction in this article.