If your TeamRaiser event has a specified Previous Event Association, your participants on a returning team will see previous events' teammates in their Participant Center by default. To change this setting, you will want to:
  1. Navigate to Fundraising > TeamRaiser
  2. Search for the event and click Edit
  3. Click on Select Event Options
  4. Click Edit Advanced Options (under Related Actions on the lower left)
  5. Click Define Misc Options
  6. Change Past Teammates Visible in Address Book of Participant
Note: you can also specify if current teammates appear in the Participant Center