One of the 6X6 wood posts that supports my 2nd story has termites. After treating it, how can I reinforce it?

My 2nd story is built on top of my exisiting first story. It's supported by 9 6X6 wood posts, 3 rows of 3 each, along the front, middle and back of the house. The back row is visible on the outside under the balcony. One of the posts there were weakened by termite. How can I reinforce it to make it as strong as before?