In Windows Phone 8, I get an email.
I want to reply to it or forward it. The text of the original email with headers is added at the bottom of the edit screen.
Is there any way to delete or edit some or all of that text in my reply or forward?
Unfortunately no :(
Your best bet is to do it through a web browser.
as an (ugly) alternative you could copy the email you want to reply to and create a new email with RE: and the pasted modified body...