HI Badey,
Unscrew the top, remove the piston and shaft assembly and wash it in a hot soapy water mix. Clean in and around the piston seals thoroughly removing all the sand and crap.
Pop the valves out of the piston and wash them also in hot soapy water. If you can unscrew the handle from the shaft do so and remove the shaft from the pump top and then clean and wash all the seals in the cap.
Reassemble everything once it is all dry and lubricate all the seals and sliding parts with Silicone spray. Same goes for the valve seals. You mayneed to reglue the valves back in with a polyurathane cement.
She'll do you right for a while again.
Good winds,