To change your password, simply log in to your account and hover over Settings located at the top of your page to select Profile & Shipping Info. To the right of Details, click on Edit, giving you access to your profile information. Select Change Password to enter a new password.
A small window will open up allowing you to enter a new password (you will be asked to enter your old password first), then click Update. When you finish, please make sure to select Save located at the top of your Details section.