How do I raise up a concrete floor to Match existing floors?

You will have to build a sub floor. Depending on how much difference between floor heights as to what size boards to use, 2x4's or smaller,bigger. You will build a grid on concrete floor then 3/4 in plywood on top of grid. Then you can install matching flooring. Be careful of measurements to match up to old floor.

Make perimeter Forms & tech and clean the old concrete & pour special “topping or leveling” concrete on top, screed & gloat it to match.

There are a lot of factors to consider. How will doors and passage ways be affected? How much needs to be filled in? Does it meet code? Here is some basic info.

https://youtu.be/VjOsBO5M6l8

https://www.proremodeler.com/raising-1960s-sunken-living-room-floor

Typically if you have a concrete floor you do not raise it, you fill it in to the desired level. Does require a building permit. I would obtain bids from licensed contractors and then make your decision.

As a piggy back on Linda Mooney's comments: Think of building it similar to a deck on top of the concrete floor.

Depending on how much the difference is and if you want wood or concrete on the area, you can pour concrete on top of concrete. However, existing has to be scored to adhere with the new and it has to be a certain depth. If you're interested in going that route, I can check with my ex. He's a contractor and had to do that to my house when I wanted to go from a carport to a garage.

Thanks for all your feedback😊