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 bottom left corner corner of the screen and select "Account".
On the resulting screen, select the "Profile" button, which will take you to the screen where all details of your profile are available:
Here, you can modify your profile's information, such as:
Modification of associated email address and password
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.
To change the email address associated with your account, or your account password, you need to visit the next section of the drop down menu - "Security":
This is where you will be able to change the email address and password that serve as the credentials for your Elastic Email account.
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.