Sometimes a hardwood board can be damaged or stained so badly it needs to be replaced. Often people would prefer to leave this job to a professional who has the experience to do the job, but since there are no special tools required to replace a floorboard, a confident DIY'er could take on the job themselves. Here's how to remove and replace a damaged hardwood floorboard.
Removing the Damaged Board
Make sure you're wearing safety glasses/goggles before using power tools.
The damaged board is held in place by interlocking tongues and grooves on its sides and ends so you can't just pry it up, you need to split the board and then remove the pieces.
Either drill a series of holes along the length of the board to be replaced or make two saw cuts 3/4 of an inch in from the edge of the board. Most hardwood flooring is 3/4" thick and you don't want to drill or cut into the subfloor so set you saw depth to 3/4". Avoid damaging adjacent floorboards by covering the bottom of your saw with tape and putting cardboard down around where you will be working.
After splitting the board, use a wood chisel or a pry bar to remove the center of the old board, then pull the two remaining side pieces into the middle (working away from the good floorboards) and lift them out. Finally, remove or sink the original fasteners that held the board in place.
Replacing the board damaged board
If you don't have a replacement board left from the original installation, you need to get a replacement board and finish it to match the floor.
Measure and cut your replacement board to length. (Your replacement board will have a tongue and a groove on opposite ends and a tongue and groove on opposite sides so, first cut off the tongue end, ensuring your saw cut is perpendicular).
You also need to remove the bottom lip under the groove along the side of the board, by ripping it at a 45° beveled angle along the bottom edge. You can make this cut using a table saw or even a sharp wood chisel and a hammer. Having the bottom cut on an angle will make it easier to slide the replacement board into position.
Test fit your replacement board ensuring it fits nice and tight lengthwise. You may need to sand/angle the bottom of the ends a little so they will slide into position easier.
Once you're sure the replacement board fits, put it into the opening by sliding the grooved end of the replacement board over the tongue end of the existing board and the replacement board tongue side into the groove on the in-place floorboard. The flat end and the side with half a groove should slide into place but you may need to use a rubber mallet and a piece of scrap wood to "persuade" it into position.
Finish replacing your floorboard by face nailing it then countersinking the nails and filling the holes with matching colored wood putty.