The best way to handle these types of information lines on your credit report is to dispute them but you have to remember that if that isn't done correctly, it is like kicking a hornets nest. Just calling them and saying, "hey, I dispute this." is NOT good enough, regardless of what ANYONE says. It has to be done with a certified, return receipt letter that has been properly worded to prevent the sleezy little buggers from using a loophole. You can find a lot of information out there about how to do this on sites from people like Dave Ramsey or with self help books like Weathering Debt (either one works, but I prefer Weathering Debt, it was much more concise and to the point) but whatever you do, DON'T try to wing it and don't pay someone to do something you can do yourself with ease and for free. Besides, you need to know how to stop the problem from happening again, right?
You don't have to pay your bill in full to have your payment count as on-time; you only have to pay the minimum (though that isn't there to do you any favors – it's there to keep you in debt: You'll be paying lots of interest, and paying off your balance for years). However, if it's all you can afford, you're better off making the minimum payment on time than not making a payment at all. The important thing to remember here is that a consistent history of on-time payments will cause your credit rating to rise.
Next, estimate your monthly spending habits for other expenses such as gas, groceries and entertainment. Create a limit, based on your income, of what you can spend in each of the different categories of expenses. For example, if you tend to spend $400 a month on groceries, try to stick to $300 a month on groceries by making changes like buying generic brands, using coupons, and resisting impulse purchases.