Sooner or later, the day is going to come when you get an unsightly blemish on your floor as a result of a cigarette burn, accidental spill or other type of blemish. Most hardwood flooring has tongue and groove joints that interlock the planks so if you have some scrap material on hand this works well. Remember when you purchase flooring to get additional material and keep it aside for times like this when you need to patch your floor. Keep in mind, of course, that some floorboards might be beyond repair and will need to be replaced completely. This is especially true for older homes. You'll find in older homes also that flooring that is near an old radiator may be stained, rotted or warped.
You can use a circular saw to remove the old floorboards. Remember to always cut lengthwise, and in the middle of the board to avoid hitting any other good boards. Remember also that cutting through the sub floor is not a good idea! To avoid this, set the depth of the cut at the thickness of the flooring. After the cut is made, use a chisel to pry out the sliced board and remaining debris. Make sure that the replacement board is as close as possible to matching the original board