If possible, you will want to desalt the ham before you cook it. Whenever possible, try to desalt the ham prior to baking, roasting, or reheating. This will ensure you are able to remove as much of the salt as possible. If your ham is too salty, dilution is a great way to remove some of the salty flavor. Take the ham and place it in a container of fresh, cold water. Cover the container with a lid or aluminum foil. Then place the container in the refrigerator for at least 2-4 hours. This will help reduce the saltiness of the ham.  You can soak a ham for up to 72 hours to remove the saltiness. The longer you soak it, the less salty it will be. If soaking the ham for more than 4 hours, make sure you change the water regularly. Replace the water every 2 hours to reduce bacteria growth. After you soak the ham, rinse it with water. Make sure you use fresh, cold water to rinse the ham. Rinse the ham completely. This will help remove any excess salt from the exterior of the ham. You can cook the ham once it is rinsed. If soaking the ham does not remove the saltiness, you can try boiling it. Cut the ham into large chunks and place the meat in a pot of boiling water. Boil the ham for about ten minutes. This can help leach out any remaining salt.  Taste the ham after you have boiled it for about ten minutes. If it is still too salty, try boiling it for another one or two minutes. Do not boil the ham for longer than necessary to remove the salt. Doing so can result in tough, dried out, or unappetizing ham.

TL;DR in Chinese:
烹饪前先去盐。 浸泡火腿。 把浸泡过的火腿冲洗干净。 水煮火腿。