You can change the password of your account as well as update the account's information any time from "Your Account" panel:
In order to update your contact information, sign in to "Your Account". Under 'Your Addresses', you will find your delivery address(es). Under "Account Settings" you will find your email address, email preferences, and other personal information.
To change your password, enter the old password followed by your new password under the "Update your password" section of the Account Settings and click Update. If you've lost your password or have forgotten your password, you can reset your password here.