Username. Change it in Settings. It is the address of your profile, so any link you have shared with the old one stops working. It is never taken from your email address: you choose it.
Sign-in email. That is the account itself, so it is not a field you can edit. Write to support from the address you are signed in with and we will move it.
College or work email. That is separate, and it is for verification only. We store the address privately and show only the domain on your profile, so people can see you are at a campus without seeing your address.