You can choose to refund the ticket and buy at the new price, if your fare conditions allow u to do so. But the refund and processing fee may cost u more than the difference.

If you bought a non refundable ticket, then you just have to suck it up.

You chose to buy it at a price which u felt you can accept. What price the company choose to sell the rest of the seats at, it's their prerogative.

The best thing you can do for yourself is to not check the prices after you have booked the tickets.