Heating times for a fully cooked ham vary depending on whether the ham has a bone in it. In both cases, preheat your oven to 325 degrees.
If the ham is boneless, put it a shallow baking pan, add 1/2 cup of water to the pan and cover the ham with aluminum foil. Cook the ham at 325 degrees for 20 to 30 minutes per pound.
For a bone-in ham, place the ham in a shallow baking pan but do not add any water to the pan. Cover with aluminum foil and cook for 15 to 20 minutes per pound.