There are two options.
1. The easiest is to request a password reset here:
This will email you a special URL and allow you to update your password.
2. If you know your current password and want to change it.
1. Click on your name in the top menu bar.
2. Click "Settings" in the drop down menu.
1. Enter your current password.
2. Enter new password.
3. Verify new password.
4. Click "Update" button.