Stop the engine and set the parking brake if your snow blower model has one. Even if your auger is not operating at the moment, stopping the engine will prevent accidental operation and reduce vibration while removing the bolt.
Push the auger shaft together until the shear pin holes align or are close to aligning. Remove any exposed broken shear pin pieces by hand.
Put your vice grip on the shear pin head and twist it back and forth while pulling up if the pin is stuck. Gently shake the auger shaft as you do this.
Place the center punch inside the shear pin hole if part of the pin is stuck inside it. Use the rubber mallet or hammer to bang on the punch and free the stuck shear pin piece.