Most retailers have a published policy allowing customers a specific time frame to receive price adjustments and an unpublished policy that actually extends this time frame anywhere from 7 to 14 days. Even if you are outside the official time frame for a price change, make the request, most stores will honor the adjustment based on the unpublished policy and because they won't risk losing a customer.
If they refuse after a 7 days period as their policy states. tell them to do a refund from the receipt and repurchase it from the receipt. this usually works because you have 90 days to return merchandise