To enhance the holding force of a vacuum gripper, one should:

The choice to increase the gripper size is accurate because a larger gripper can create a greater surface area in contact with the object being held. This expanded surface area allows the vacuum to exert a more substantial holding force, as its effectiveness relies on the difference between atmospheric pressure and the pressure inside the vacuum cup. The larger the vacuum cup, the more air is displaced, leading to a stronger grip on the object.

In contrast to this, decreasing the vacuum level would reduce the pressure differential, thereby weakening the holding force. Removing cup reinforcement might also reduce the structural integrity of the vacuum gripper, potentially leading to failure during operation. Lastly, choosing "All of the above" would imply that all options are viable methods to enhance the holding force, which is not correct, as only increasing the gripper size directly contributes to an increase in holding force.