You shouldn't have to replace the flint of stuck flint wheels. Normal flints mechanisms have three parts: a spring, a flint, and the flint wheel. When new, these parts can stick, preventing sparks needed to ignite the flame. To resolve this issue:  Open the lighter. Remove the insert from the lighter case by pulling on the insert by the flame guard, which is the raised part of the insert with holes in it. Remove the flat head slotted screw fastening the flint spring at the bottom of the insert by turning it counterclockwise with a screwdriver. Pull out the screw and attached flint spring. Tap the top of the lighter to knock the flint loose. Replace the flint, spring, and refasten the screw. Your flint wheel should be unstuck. Pull the lighter insert from its case. Turn the insert upside down. You should see the brass screw fastening the flint spring. Unfasten this with a screwdriver or the case of the lighter. While keeping the bottom of the insert oriented upward, pull out the unfastened screw and attached flint spring. Tap the insert gently into your palm to knock loose the flint so it falls into your hand. The flint will look like a very small cylinder roughly the size of the flint spring tip. Old flints can be thrown away. While holding the insert so its bottom is still facing upwards, drop the new flint down into the flint hole. Reinsert the spring into the hole and refasten the screw. Replace the insert back into the case. Make sure the case is seated correctly by closing the case. When the insert is correctly positioned, light the lighter as you would normally. If, after replacing the flint, your lighter still doesn't work, it might be out of fuel. Check and refill fuel as necessary.

Summary:
Unstick stiff flint wheels. Unfasten the flint screw at the bottom of the insert to replace the flint. Remove the flint. Replace the flint and reassemble the flint mechanism. Test the new flint.