To change your personal information, just log in to your account, and select the cogwheel ("My Account").
This screen will show you your account information and allow you to amend any personal details, such as your registered email address, password or address.
Select "Edit" next to the field you wish to change. Then submit your new information and "Save".
For more information on how to select a secure password, please visit our article What should I consider when choosing my password?