i did some google. it turns out you using GW1 account ?
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DISPLAY NAME ISSUES:
- We may allow players to change their own Display Names in the future, but it's not possible right now. We don't have an ETA for this just yet, but we are working getting it working as soon as possible
- If your display name is showing up as long string of numbers and letters on your account management page, there is a good chance you logged into account management using an account that only has a Guild Wars 1 account on it. This will show your display name as numbers as the display name is meant to be used with a Guild Wars 2 account. Since you haven't set up a GW2 account and linked your GW1 account to it yet, you don't actually have a GW2 display name set. Luckily this is really easy to resolve. Once you purchase Guild Wars 2 just follow the directions at http://support.guildwars2.com/app/answers/detail/a_id/8982 to register and link your GW1 account with a GW2 code. When you do that you will be given the chance to select a display name. After you complete the registration process your display name will update from that number to the name you select.