You can do either, or both. Try pulling out the shabby blades first, by using a pair of rubber-coated gloves, for gription. If they come out easily, and the clump looks better, you can let that suffice.

If they're too far gone for that, trim them off to a couple of inches. They'll grow back a fresh flush of new foliage. It'll happen pretty quickly if they are indeed gool season grasses. If they're warm season grasses, they won't start growing back until later, but will still fill back in nicely.