For example using file: UserPreferences.ini (within /Dungeons and Dragons Online/ folder - same one where your DDO screenshots go depending upon your OS)
Code:
[User_1]
UserName=your_login_name
WorldName_1=Thelanis
LastPlayed_1=2016-09-24T00:04:00
UserFileName_1=en-DDO-EULA-Turbine-html
UserAckTime_1=2013-11-14T14:13:00
UserFileName_2=en-DDO-TOS-html
UserAckTime_2=2013-11-14T14:13:10
WorldName_2=Lamannia
LastPlayed_2=2016-09-01T12:00:00
It should be safe to delete that specific text under the UserName line, and the game will rebuild those login lists when you you login to a specific world. Your list will look slightly different (i.e. Worlds/times listed)
Do NOT delete all [User_1] or UserName=your_login_name of course your own login name will be there not the place holder in my example. Albeit it should be safe; just to delete your own username after the: "=" equals sign symbol.
For example the line starting: UserName=Zhijie would become: UserName=
Of course make a backup copy of the file first and save it with the correct [*.ini] extension and ONLY delete the lines I've mentioned, etc.