Just to be clear, there are 2 issues removing a floor board.
First you need to cut across the board at the end of the section you wish to remove. This should really be done on top of a joist. You may see a previous cut close by that you can utilise. If not you have to identify the joist and cut there, by definition there will be nails there so circ saw not ideal. A multi cutter or spiral saw will do the job or go old school with a pad saw. You may need to chop off the tongues as below for about 500mm either side to prise up the board in the middle of a length.
Next you need to cut through the tongues on the edge of the board. If your prop is old, natural shrinkage should leave a gap between the edges allowing access, if no you have more of a struggle. Usually a 2 1/2” bolster chisel is best way. Chop down both sides and prise up from the cut end, putting a bar under board as you prise to support the board against springing back. Every time you reach a joist, extra effort needed to prise up fasteners. When u get to last joist after the point were u want to remove, cut board in line with joist.
If your cuts are not over a joist you will need to fasten a block onto the joist to support the board end.
Once one board section is removed, adjacent boards are easy as you won’t need to deal with the tongues.
