Yep, do your next water change with lower salinity water. And be sure that you are only topping off evaporated water with totally fresh water, not saltwater. Salt does not evaporate, only the water does, leaving the salt behind. If you do not top off with fresh water, your salinity will go up.
depending on how high it is...... lower it slowly..... large changes will stress the inhabitants and cause cause problems with them..... even death.....
remember....... NOTHING GOOD HAPPENS FAST IN A REEF TANK!
Yote has a good idea there, to slowly adjust it. Just for what its worth, An investment in a Refratometer would help salinity issues. I have yet to find an accurate hydrometer. If you cant afford a refractometer try finding someone who has one and check your hydrometers accuracy with it. Hydrometers cause alot of stressful problems with tanks as they are usually off alot.