My yahoo mail login username/password is saved on all pcs I login to at uni. How can I remove this?

I've tried making a new password. I only need to type the first letter of my email address on any of these pcs and then the full email address is on the dropdown menu, if selected, my password is automatically entered. I've got two emails from myself recently that I didn't send, hence why I'm worried, even if the information is only tied to my personal login to the uni network.