Change of email address but not internet provider

My problem is that I have changed my email address only and whilst I can log in to the email I cant download or send any emails from the software. I am needing help of what to put in which fields to make it work. Thank you. 

The easiest way if you are using IMAP or Exchange is to remove the existing account, and then add the new one.

If you want to move your emails from the one to the other, then add the new account, move the emails across, then delete the old one.

Yes whilst I agree with what you say, I have emails that I dont want to lose (quite a number).