Go to People, find the contact you want to edit, touch them for a second. When the contact comes up with the numbers and email address, touch and hold the number you want to be the primary contact number for a few seconds and you will see a larger card pop up. One of the choices that will pop up on that card will be "Set as Primary Number".
I don't have any contacts with more than one e-mail address but, the same process would probably apply to the e-mail addresses as to the phone numbers.