I have a Samsung Galaxy S II
After struggling with changing my yahoo password, I decided to install the full yahoo mail app, and delete my current access within the email app.
Learned that downloading my contacts may not be the best choice, and that there wasn't an easy way to stop the loud and annoying sound alert for arriving email from the yahoo emaol app. Uninstalled it.
googled email pop settings
copied down info:
pop.mail.yahoo.com (port was wrong, should be 110)
smtp.mail.yahoo.com (port was wrong, should be 587)
tapped on email
could see existing email account, then pressed [=] button
which revealed Compose/Add Account/Delete Account
tapped on Add Account
user name is full
emailname@yahoo.com
Does incoming and then outgoing, then finishes with specific options
Enjoy
(this took place over a 2 day period)