New from reddit:
It is now possible to change the account name you use to log in to GW1/GW2. So if your login email address is an old address you don’t use anymore, you can now fix it.

1. Login to https://account.guildwars2.com/account
2. Enter a new email address and your current password.
3. Confirm your new email address

This will also change your Guild Wars 1 details if your accounts are linked.