Go to Tracfone website and buy 1GB of data online for your smartphone. Use promo code 66975
to get 500MB free data. Make sure it says "Promo Code was Applied" before you complete the purchase.
As usual with Tracfone, it may be awhile (10 minutes or more) until your added data is reflected in your balance.
UPDATE: I placed two separate orders with the same phone for 1GB with the promo code and got 1.5GB for each order so the promo code should work at least twice.
UPDATE 2: Get 1.5GB for $8 (YMMV) (thanks MidwestMomma): Add 1GB to cart, add another GB for $8 more, remove the original 1GB for $10, apply promo code & check-out.