To edit your profile, start by selecting your profile page from the top right drop down menu:

Then select the "Edit Profile" button in the far right:

This will take you to the profile editing and settings page:

You can add and delete your Twitter, Facebook, and LinkedIn accounts tab on the left hand side of the page.

To add an account, click on "Connect account" next to the respective account. You will be redirected to a seperate authorization webpage to enter in your login and password for that service. To remove an account, click "Remove connection" next to the respective account.