You have the ability to change your account's credentials at any time. In order to do so, open the drop-down menu with your account name in the upper-right corner of the screen and select "My Account". On the resulting screen, select the "Profile" button, which will take you to the desired screen with credentials:
Here, you can modify your first name, last name, phone number, address, Zip/Postal code, city, country, company name and tax ID number.
As long as you are the owner of the account's email address, you will also be able to change it with the help of a confirmation email that will be sent to the current email address. Please note that it would also change your account's login.
It's also possible to change your account's password this way. When you change your password, you have the option force all currently logged in devices to log in again with the new password.
Keep in mind that when you send an email signed with certain credentials, this identification information has to be valid for 60 days in advance.