Your medical plan is listed on your ID card (digital cards are available at UMR.com) and the THT member portal.
Look for Signature Plan or Advantage Plan in the lower left-hand side on the front of the card.
You can switch your plan during the annual open enrollment period (typically in October/November) or any time during the year after experiencing a Qualifying Life Event (requests must be submitted within 60 days of the Qualifying Life Event).