Revolving accounts don't hurt your credit any more than installment credit accounts do. However, what you need to keep an eye on – instead of just revolving vs installment – is in how much credit you're currently using.
One part of your credit score is the utilization ratio. The credit utilization ratio refers to how much of your available credit you are currently using. A ratio that's over 30% can harm your credit score.
If you're not sure what your utilization ratio is, just divide your total credit card balances by your overall credit limits (make sure you include all of your different lines of credit via credit cards, if you have more than one).