If there is a wall dividing the rooms and it's load-bearing, you'll have to replace it with a beam or pillars when you remove it. It's always best to hire a professional to do something like that, though!
Load bearing wall is best left to the pros.
Remove no load bearing wall.
Make them flow into each other with color and like furniture
Typically it involves removing walls or opening up doorways to physically open the rooms up to each other. HERE IS A POST I wrote showing just that in my son's and DIL's house. They opened up a 1970's house to create a farmhouse open concept.