Hi friend,
If your led has a regulator for power than you don't need to change height but regulate intensity.
If your led has no regulator for power I would advise 50cm for seedling stage and let it decrease as you go.
Download a app called photone. It will tell you the strength of the light. Place the phone level with the canopy and see what ppfd its showing. Aim for about 100ppfd in seedling stage.