Keel Bolts

Bonjour! First post on here but have been reading a lot and this site has been extremely helpful! 

I wanted to see if anyone knows anything about how the keel bolts are installed? I have two keel bolts that are rusted. I took off the nut of another keel bolt and see just the stud. I’d like to replace all the keel bolts if that’s feasible but not sure how to go about it. Don’t want to damage anything!