You can edit your account in the Account page. You can change your real name, e-mail and password. You can also set the preferences.
Some sites require you contact an administrator to change your details. In this case, the Account page allows you to generate a hash to let your password be changed securely (your administrator cannot recover the password from the hash).
The real name is not changed on the posts already created.
If you want to change your username, you must contact an administrator.
In order to enable the “Show me posts by other users by default” preference, you must first have the “can edit others’ posts” permission.