In order to change your password or e-mail address, you will have to click on your username tab on your upper left side. Several options will drop down and you will have to click on 'Profile'. When you click on this option, you will get a dialog where you will be able to see your profile details. On its upper right corner, you will see an "edit" button. If you click on this button, you will be redirected to a webpage where you will be able to edit your profile.
On the upper right corner, there is a tab called 'Settings', if you click on it and scroll all the way down, you will find the options 'Change Password' and 'Change Email'. Click on any of those two options and change your password/e-mail address.
We also highly recommend to complete your profile details so other users can know a bit more about you. Read more on how to complete your profile here.