If the lights work, then you can just swap out the lights...if the wiring is bad, then you'll have to think about where you want your new lights and HOW you want to get the new wiring there. I had to make new runs for by cabin lights. They aren't perfect and I've seen some guys on this site with better ideas.
I bought 5 1/2" dome lights from Marineengine.com for about $35 and a couple of reading lights for the fore cabin. They were all LED, I left the a regular lamp in the head because I figure it would only be on while in use. I have to 'center' the reading lights in the fore cabin...
I also installed a little 3 LED amber light behind the steps for at night and I bought 5 or 6 18" LED amber light strips on EBay and installed them behind the headliner ridge. They are hidden from view but I have those amber strips, the step light and a red LED light in the cockpit wired to a seperate switch for nights. They create a great warm light and I don't really need to use any of the cabin lights unless I'm down there.
I would just search "Marine LED lighting", you'll find a bunch of sites...Defender, Jamestown, SailorSams, etc that offer great deals. It's all about the cost plus shipping to where you live.
Good luck!
Chris