The easiest way to lower the salt levels in your aquarium if your hydrometer is reading higher than expected is to perform a partial water change. Depending on how much higher than it should be depends on how much water you need to replace.  If you remove 10% of the aquarium water and add RO water (Reverse Osmosis) in its place then re-measure you salinity with the hydrometer. If you find you have replaced slightly too much and the levels are low. Mix a small tub of RO water with your salt and add small amounts slowly.

Ensure than you never add the salt directly to your aquarium as this can have serious effects to your live stock due to a built up on concentrated salt in specific areas of the aquarium.
Over time you will become used to the amount of salt you use when performing a water change and it will become natural to you. Try and monitor how much water you are losing through evaporation on a weekly basis as this can affect your salt content in your aquarium.