You can make the username and password fields not required by changing a TeamRaiser setting.
  1. Select Fundraising > TeamRaiser
  2. Find your TeamRaiser and click Edit
  3. Click Select Event Options
  4. Under Related Actions, click Edit Advanced Options
  5. Click Define Event Options
  6. Under Registration User Name/Password Assignment, remove the check mark next to "Yes, administrators may enter the user name and password for a participant they are registering"
  7. Click Save