You need to resurface the head
https://www.youtube.com/watch?v=L1jFtTzLh7o
And here's how to replace the head gasket
https://www.youtube.com/watch?v=iuD8pzCe6aE
I HIGHLY recommend getting a Kohler head gasket with the "fire ring" ( sheetmetal ring around the combustion area ).
It MUST be retorqued after you run it the first time.