Always mix your saltwater before adding it to the tank and check your salinity. Luckily, this was an opportunity to learn since the tank is new, but when you add livestock to the tank, adding salt and water like you did would kill them (the salt can actually burn fish and inverts if not mixed completely. If you've ever gotten it in a cut, it stings like H***!). For future water changes, invest in a good sized bucket to mix in and an extra pump and heater. Use the pump to create circulation and make sure the salt dissolves completely, and the heater to get the water to the right temperature before adding it. The process usually takes at least a few hours depending on the amount of water you're preparing. Do you have any water circulation in your tank? Powerheads? Return outlets? If not, the salt is going to take a long time to dissolve.
What is your current salinity? It's hard to estimate how much water to take out if you don't know how much salt is in there.
ETA: if you're using one of those weighted tube style hydrometers, and it's an inch above where it should be... You added WAY too much salt. What is the number reading on the hydrometer? The packages that the salt comes in generally gives you an estimation as to how much to add per gallon that will get you into the average salinity range (I know Instant Ocean says 1/2 cup per gallon). Did you read that recommendation? You're probably going to have to take out at least a few gallons of water and replace it with plain RODI or distilled water.