You have paid $170 pp for each ticket. You will be charged another $100 per ticket if you make a change. (If they change the flight or lower the price of the exact flight, you can get a credit, but that's THEM making a change to the flight price, not you, and not to the flight itself.) The change fee is going to more than wipe out any difference in fare. You'll be left with a $70 credit to apply to a new flight...$170 for the existing ticket minus the $100 change fee equals $70 remaining.
The tickets you are looking at switching to are $145, and you'll be able to apply the $70 credit per ticket leaving $65 MORE per ticket that you owe. Is it worth the additional $65 per person (the net difference in the change fee and then lower price of the new ticket)? Depending on where you live (if the Hartford flight is more convenient), it might be worth it...$235 total out of pocket per person isn't horrible.