DIAGNOSIS: Blender blades don't get "dull" like knives; they bend or chip. More likely, you're overloading the jar or not using the proper technique for the K150's design.
FIX: Technique first: Use the Pulse function in 1-2 second bursts, not continuous run. Add at least 1/2 cup of liquid for ice crushing. Don't fill the jar more than halfway with ice cubes. Ensure the jar is firmly seated. If performance is still poor, inspect the blades for obvious bending or damage.
IF THAT DIDN'T WORK: If blades are visibly damaged, the entire blade assembly is sealed in the jar. You cannot sharpen or replace just the blades. You must purchase a new replacement jar from KitchenAid.
HEADS UP: The K150 is a mid-duty blender. It's designed for casual ice crushing, not professional-grade frozen drinks. Attempting to crush a full jar of solid ice will stall it and damage the motor over time.