To reduce calluses, I would suggest using moisturizing cream daily. Also, every few days soak your feet in warm water and use a pumice stone to scrub off the thickened skin layer. Be careful not to be too aggressive. Removing live skin could cause bleeding and infection.
If your corns or calluses become painful, then see your podiatrist or foot specialist. We can trim down the area and evaluate any structural issues you may have and make individual recommendations. Bunions and hammertoes often have calluses as a result. There are shoes and supports that accommodate these features and reduce friction and pain.
Diabetics should especially work with their podiatrist to manage the long-term health of their feet and to reduce the risk of bleeding, infection, and complications. If you have poor circulation or neuropathy in your feet, only a podiatrist should resolve your calluses.
To keep corns and calluses from returning, wear shoes that fit well, wear socks that firmly conform to your feet, and try to accommodate any prominent features of your feet. Reducing the rubbing on your feet should keep them happy and out of your doctor's office.