Wood flooring that has some boards swollen due to moisture can only be fixed in one way: The bad boards need to be replaced. Getting them out is a challenge because you don't want to rip the tongue-and-groove edging off the neighbouring boards. Getting the new board in is also complicated, since you have to cut away the bottom of the groove on the board in order to set it. See your floor dealer for replacement boards the same size and style as the ones you're replacing.
Sit your saw on one of the replacement boards to set blade depth to the thickness of the boards, usually between 1.2 and 1.5 cm (1/2 inch and 5/8 inch).
Use the saw to cut multiple lines up the middle of the first swollen board. Cut them side by side initially, then cut some lines crossing into others. Don't cut into the edge of the board at any point. Continue until pieces of the board are coming out, so you're hollowing out the body of the board. Pull away the cut pieces.
Force the edges of the board in toward the empty middle of the board, using your hammer and chisel. Work the board completely out, without damaging the boards next to it.
Lay the new board facedown on a flat surface. Cut off the half of the groove that runs along the length of the board, using a razor knife.
Set the replacement board into the open spot, tongue-side first. The grooved side should drop right over the neighbouring board because of the missing bottom half of the groove.
Secure the board by shooting nails every 25 to 30 cm (10 to 12 inches) along the sides with your nail gun. Do the same for each of the swollen boards that need to be removed.