You've already gotten some good answers. With all due respect to Dave Ramsey, please ignore - for now - the ones that say you don't need credit. Unless you're in a position to pay cash for a house or a car - and it doesn't sound like you are - then you WILL need credit.
The length of time that you've had an active account with a creditor is an important part of your credit score. I have accounts still open that I opened in college and I haven't used them in years, but they show 14 years of good credit history. So if you do move to a new account, don't close the old one. If you are carrying a balance on a card and the introductory rate is about to expire, call up an old account that you had (and kept open) and see what they'll offer you for a transfer balance. You may be able to get a low rate for a few months. As someone else answered, spread your balances around if you are getting too close to your credit limit on one card.
At the end of the day, you really do need a plan for ending the credit card game. The best way to use a credit card is to only charge what you can pay off each month and earn rewards. My mother is very disciplined and charges $800-$1000 a month in gas, groceries, and other shopping but she also budgets the same amount every month and pays the bill in full. In the meantime, she's earning points on all of her expenses. Most of us aren't disciplined enough to do that though, so switch to lower interest when possible but be aggressive about paying down that balance and keep your old accounts open. Then settle on one card with reasonable interest and good rewards to use judiciously or in an emergency.