To make changes to your account, sign in to the app using your email and password or connected Facebook account. Once signed in, click your screen name at the top of the app and select "Account" to access your profile. To change your password from the profile page, scroll down to the password field and click the "change password" button. You'll need to enter your current password, then the new password twice to confirm. Finally, click the "save" button to save the changes.
Please note that if your account is linked to a Facebook account then you cannot change your password; in this case you'll need to unlink your account from Facebook by clicking the blue "Unlink" button at the top of the Profile page, or you can go to Facebook and change your password there.
If you'd like to change the email address associated with your account, you can follow the above steps to reach the profile page but instead click the 'change email' button.