Your inside coils are blocked with dirt. You will have to slide out the blower and clean the fan blades and you will have to spray coil cleaner (liquid sodium hydroxide) on the coils and clean with an electric pressure washer (1500 psi). On smaller units 2 1/2 tons or below you can use a water hose sprayer. It's a messy job, but it's the only way to fix the problem. If you were an HVAC mechanic you could remove the coils and pressure wash them. You will need to clean out the drain line, too. Make sure to clean outside unit, too.