To change your password, username, or to make any other changes to your profile, just click on the "My Profile" link in the grey box at the top left of the page.  Next, click on the "Edit" tab to access your account information.  

Changing Your Account Information

When you first enter the "My Profile" page, you will be on the "Account" tab.  From here you can change your username, password, and userpic.  You can also delete your userpic if you're not happy with it.

Note that some browsers will try to automatically fill in your password information.  If this happens and you try to save changes to your account, the site will think you are trying to change your password and will prompt you to fill out both password fields to confirm the change.  If this happens, simply delete the text in the password box (thus keeping your old password) and click "Save" again.  Your intended edits should go right through.

Changing Other Parts of Your Profile

There are two other tabs on this page, "intro" and "personal information."  Click on "Intro" to change or update your answers to the questions about you and your writing we asked when you set up your account. Click on "personal information" to change your name or to change or add the URL to your website, blog, etc.