what to do about swelling on feet and ankles on a 76 yr old man? (he is not overweight)?

sounds like congestive heart failure( CHF) he likely needs heart medication and some exercise, support hose can help, he may need to see a cardiologist to check his veins and arteries

raise your feet above your head

Maybe restricted blood circulation. Does he have a varicose veins problem? Raising the feet to heart level helps the blood flow. Common problem with old age.

This doesn't sound like a skin condition. Feet/ankle swelling is often related to either the heart not pumping efficiently or other organs not processing waste correctly. Your best bet would be to get him to his regular internist to refer him to the specialist for whatever organ is causing the issue. i.e., cardiac, pulmonary, nephrology for starters. Generally it means something is not working properly and a doctor visit is called for.

See a podiatrist.

If you want, you can try one of those boot things that’s supposed to help with better circulation.