A Big Misup

I am not good with computers. I downloaded the free e-mail client, I did manage to get it on there. But when I send e-mails my password is on there. How can I get it off or does it have to be redone? My password to my email accounts is on the email cllient. Everytime I send out a email everyone gets my password. So I try not to send out any emails until I can get this fixed. Can someone tell me how to fix this mess.

could you please send me an email so I can analyze it? Thank you.