Turn the filter off by switching the main dial to the "Closed" or "Test" position, ensuring that water will not be pumped into the filter system from the pool while you are changing the sand.
Unplug the filter drain to allow all the water currently in the filter system to flow out of the system's pipes.
Disconnect the dial valve at the tank flange and remove the water diverter that directs water into the filtration system after it is removed from the pool. Extract the basket assembly that conducts the housing for preliminary filtering to gain access to the sand filtration elements.
Vacuum the sand out of the filter with the wet/dry vacuum. Vacuum gently to avoid damaging more-delicate filtration components.
Cover the stem drain so that newly added sand will not fall into the stem pipes, where it might contaminate the pool.
Add new sand up to the level indicated in the filter container.
Uncover the stem drain and replace the basket assembly, water diverter and dial valve. Finally, turn the pump back on to re-engage the filtration system.