Please login to your account and follow the below given procedure:
1. Once you have logged in to your account, please click on "My Folder"
2. You will be directed to your Bookshelf. Then Click on Profile Settings
3. You will get a drop down with few option which will also have the Change Password option. Please click on that to change your password.
4. Put in your Old Password and the New Password.
If you do not remember your old password, please click on the Forgot Password link to get a password to your registered email address.