The username that appears is probably derived from your network/computer login; however, you may want something different like your first name or your standard GoldMine login.
If you do a Right-Click > Properties on the GoldMine shortcut on your desktop you'll see the Target field, which will say something like "C:\Program Files\GoldMine\gmw.exe"
To override what's in the username field when logging in, append a /u:USERNAME to the end of the target, so that it reads like this:
C:\Program Files\GoldMine\gmw.exe /u:jen
You can also input your password here as well, like this:
C:\Program Files\GoldMine\gmw.exe /u:jen /p:password
Tip: Note the direction of the slashes, and the spaces between the Username and the Password.