To start- you will need to go to your account page. You can get there by clicking on your name, in the upper right corner of the app.
Click on 'View Profile', you'll be redirected to your account page. From here you'll be able to change your name, email address, and password. Additionally, you can change your payment method, and even downgrade or upgrade plans any time you want.
Keep in mind that in order to change your details you'll need to re-enter your password so the changes take effect.