You can change your user settings at any time by clicking on the Settings link in the top-right menu of Piwik, as shown in the following screenshot:
The first page that loads is the one to edit your user settings. At the top is where you can change your basic settings. This is shown in the following screenshot:
Here you can change your e-mail address and password. Once you change your password, your API token for Piwik will be reset and you must add your new API key to any software that requires it.
You can also set the default reports to load in your dashboard. You can choose the All Websites dashboard or the Dashboard for a specific website. Below that you can set the date and date range you want the reports in your dashboard to load by default, as shown in the following screenshot:
Below that is a link, that when clicked on, will exclude you from being tracked by your Piwik installation. You just click on the link and Piwik will set a cookie in your browser...