The only way you can get your credit score improved quickly is by hiring a credit repair agency. Make sure it's a reputable credit repair agency that is well known for repairing peoples credit.
Also if you owe a bill and it's sent to collections and a collection agency calls you demanding you pay up then don't pay the collection agency as they can actually ruin your credit even more.
When a bill is sent to collections the company that you previously owed the money too has written your account and money owed off as a loss and you no longer owe the company any money.
The credit agency buys your debt for less than you owe and that's how they make a profit and can give you an offer to pay less than you owed originally to the company.