What can and DOES change is whether you have a collector pursuing you for the debt. If you are talking about a dormant account that has been in collections and has finally been left alone with no collections activity for a few years, messing with it can be problematic from the point of view that the collections people will start pestering you again to see if they can get money and if the SOL isn't up, they can start reporting on it again which can affect your score or they could even file suit if your state SOL isn't up.
This is easier said than done, but reducing the amount that you owe is going to be a far more satisfying achievement than improving your credit score. The first thing you need to do is stop using your credit cards. Use your credit report to make a list of all of your accounts and then go online or check recent statements to determine how much you owe on each account and what interest rate they are charging you. Come up with a payment plan that puts most of your available budget for debt payments towards the highest interest cards first, while maintaining minimum payments on your other accounts.