Click 'Sign In'/'your account' button > 'Sign Out'.
If signed in with your UQAT ID, you will see a page titled 'To complete logout, close your browser', prompting you to close the browser to fully sign out. If you do not close your browser and return to the main search page, you will see that you are still logged in. If you signed in with your barcode, you will be brought back to the main discovery search box, and are not required to close your browser to complete the process.