The Logout function is located in the top right corner of the Header. It is part of the User Credentials module, showing the user ID with which you have logged on the Portal.

This is for display only, you cannot directly edit the content of this field.

The only possible action here is to click on the LOGOUT button, which will terminate your Portal session in a clean and secure way, close the Portal window and bring you to the Network Manager section of the Eurocontrol website.