To change the login details for your account, click the tools icon at the top-right of your account, and select Settings & billing. Click the Profile tab, and click Edit. Type in your desired username and password, and save your settings.
Or, if you aren't logged into your account and have forgotten your password, go to the login page and click the Need to reset your password? link.
Your account's time zone setting will affect the timestamp on saved and sent mailing, as well as any mailings you schedule.
To change your time zone setting, click the tools icon at the top-right of your account, and click on Settings & billing. Click the Sender info tab, and click Edit. Select the appropriate time zone using the options in the dropdown menu, and click to Save your changes.