Pacemaker Boat Owners Association

I have just joined this site and it seems very informative, thank you for the info thus far.. So, I have my first question, it might be easy for some but hard for me, because I don’t want to screw it up nor can’t find a replacement.
I purchased a 1970 43’ Pacemaker, at a great price and there are just odds and ins that need updating or replacing. I have the two docking lights in front of the boat, I have power to them but the lights don’t work. So, removed the lights to replace them, after I took them out the casing looks like it should screw out to remove the bulb, but I have been unsuccessful unscrewing the casing. So, I’m wondering if you are suppose to purchase the complete casing with the new bulb or does it screw apart.. And if so where would I find them?

Thank you, as a new member.