It depends on what type of lamp is in the fixture. I used to run into this issue occasionally working at a lighting showroom. The answer can be as simple as making sure you use a light bulb with the correct voltage. No need to change wires, etc. Bulb just needs to be the same voltage to be compatible...this is typical for your standard incandescent light bulbs like an A-lamp...or Edison lamp. This is NOT going to be the case if you have low voltage fixture a transformer involved. In that case you would have to change out the transformer to one capable of handling a different voltage load. Stick with line voltage fixture, and simply making sure the bulb you use has the right voltage, it's a pretty simple fix.

fragle0 ... congratulations on the new addition to your family. Have been following your lovely changes. You probably won't have time to work on the decor for a while. Just wanted to suggest that you try pulling the nesting tables forward to be more in line with front of the chairs & placing your floor lamp to the back of them. This will give a bit more light at night for reading in that area.Also switching the plant by the fireplace & the one on the corner by the sofa.

if you're not going to center the dining room table under the light, then I'd tend toward a flush or semi-flush fixture, to de-emphasize the alignment. You might want to remove the medallion from the ceiling too. As for the kitchen it looks like you have decent overall lighting -- maybe you're looking for a couple of pendants over the island? simple glass globes, maybe? here are a few styles to start you out.

Please, please, please, don't paint any of the wood. You have a beautiful setting for mid century modern décor. I can agree with removing the carpet from the stairs, however I would just want to add a jute floor covering for the stairs after. The light fixtures should probably both be changed. You even have a lovely roomy space in your foyer. I always recommend starting with the foundation of the room, which is the floor covering. Kilim, ikat, Persian or Oriental would be my choice. I would think minimalist would be very fitting in this space.