I just signed up with yahoo.I want my full 1st name to show for recipient but only my initials show.?

How do I get my full 1st name back on my emails. Also, I checked block to keep me signed in for 2 weeks.When I sign out, will the user ID not hold.My other email acct in past popped-up each time & only pword entry needed. Thanks for helping this somewhat computer illiterate user.