Soil pH is the measure of the acidity or alkalinity of a soil, numerically equal to 7 for soils with a neutral pH, increasing with rising alkalinity and falling with increasing acidity. The soil pH scale commonly in use ranges from 0 to 14.
Soil pH is not fixed; you can take measures to alter soil pH. If soil pH needs to be lowered (i.e., the soil isn't acidic enough), apply sulfur or commercial fertilizers containing ammonium-N. If soil pH needs to be raised (i.e., the soil isn't alkaline enough), apply lime.
Fortunately, the Web has online calculators to help you determine how much lime or sulfur you would need to apply, given the size of the area where you are attempting to raise or lower soil pH. Here are two of them:

