Replace worn deck boards.
It's not unusual for several decking boards to be damaged on a deck that is otherwise in good condition. Replacing a board or two is not difficult. New boards, if they are of the same type as the old ones, may blend in color with the old boards after a year or two. If you clean and refinish the entire deck, the new boards will likely blend in right away.
To refasten boards, it may help to use deck screws that are 3-1/2 or 4 inches long.
Opening the gaps
Decking boards should have 1/8-inch-wide gaps between them so that water can seep through and the deck dry out after a rainfall. If a gap is filled with debris, clean it out with a stiff broom. If that doesn't work, use a putty knife. If cleaning isn't enough, widen a gap with a circular saw.
An hour or two for most deck repairs
Hammer, drill, flat pry bar, taping knife, cat's paw, circular saw, jigsaw or reciprocating saw
Making straight cuts in boards that are fastened, fastening with nails or screws
Inspect the deck for damage to framing, and plan to make additional repairs, if needed
Decking boards, nails or screws
If only part of a long board is damaged and you don't want to replace the entire board, replace a section at least three joists long. Use a jigsaw to cut on the waste side of the joist. Begin the cut between the boards and curve into a perpendicular cut; reverse cut to finish.
Draw it down with a screw.
Warped boards often can be tamed with a stronger fastener. If you don't mind the appearance of an extra fastener head, drill a pilot hole and drive a screw next to the existing fasteners. For a neater look, remove the old fasteners and drive screws that are at least 1 inch longer than the old ones.
Hold it with an angled screw.
Another option is to force the warped board down and drill a pilot hole at an angle. Drive the fastener. If a board does not lie down all the way after refastening, wait a week for it to become partially flattened and try driving the fastener (or an even longer one) again.