Like many websites, Tumblr lets you log in to your account and stay logged in as a convenience. However, if you work on a public or shared computer you may not want to remain logged in permanently, leaving access to your account open to anyone else who uses the computer. Unfortunately, as of June 2011, Tumblr does not provide an option to automatically log out of your account, which means you must do it manually each time.
Navigate to Tumblr.com.
Click the logout icon in the upper-right corner of your Dashboard. It resembles a computer's power button.
Click OK when prompted by Tumblr to confirm that you want to log out of your account.