Delete the Yahoo app from my phone? .?

I got sucked into loading a Yahoo app on my smart phone by promising that I would not need a yahoo password to log into my yahoo account. Now when I want to sign into my yahoo account to see my portfolio, I can't use my password, instead I have to run to my phone to get a new code each time to sign in. How do I get back to the old way of logging in with my password? In other words, how do I delete an app from my phone? It is a total waste of my time.