How do I change my display name in my email account ?
Depends how you are sending it.
If from webmail, click on your username in the top right corner, select settings, select profile, select edit. Change it to whatever you want displayed then click save. If from a mail app or client, you need to specify which one.
Thanks @licquorice in bt webmail and bt app my profile name does not match my display name in the from field when someone receives my emails
I never use either, but worked for me as a test with webmail.
What name is being displayed for you? Don't post the actual name, just the format.