The high-end, $60/month Metro Flex plan specifically includes this upgrade capability after 12 months.
If you are leaving another carrier, Metro offers promotions to pay off your old phone when switching. metro pcs buy back program
Trade in Your Phone: Check What It's Worth | Metro by T-Mobile metro pcs buy back program
Metro also provides a way to reduce your monthly bill by playing games or taking surveys, which can be used in combination with savings from device upgrades. Crucial Details and Tips metro pcs buy back program
If you change your plan or your service is suspended due to non-payment, the upgrade eligibility timer resets. Metro Flex Upgrades
Once you choose a new device, Metro will provide a trade-in estimate based on your old device's value.