If you feel you can responsibly handle higher credit limits, you can ask a lender to increase them — typically without damaging your score. In fact, you might even bump up your credit score by raising your total amount of available credit, thereby reducing your credit utilization ratio (if you maintain your spending levels, that is).
However, a creditor may run a hard credit check on you while evaluating whether to approve your credit increase request. Too many inquiries in a short period of time can hurt your score, but if this is your only inquiry in a while, your score may not go down or only drop by a few points.