When you log in to your app, by default, the app saves your login credentials and the server URL. However, you can switch off this setting. Also, after you have logged in to the app, you can change the login user and server URL without requiring to log out. You can do this on the Account Settings tab of the Settings screen.
To go to the Setting screen, tap the Settings button at the upper-right corner of the Home screen. The Account Settings tab displays, by default.