The soil pH is important because it affects the availability of nutrients in the soil. Many plant nutrients are not readily available to plants in highly alkaline or acidic soils. These essential nutrients are most available to most plants at a pH between 6 to 7.5. Nevertheless, some plants such as blueberries need acidic soils, but others need alkaline soils.
Consequently, to improve your soil pH you have to consider what kind of plant is growing.
Plants that require a more acidic soil than they are growing in will often signal this by developing iron chlorosis, a deficiency that causes the leave veins or entire leaves to turn yellow. You have a couple of options: Sulfur, Iron Sulfate, Sphagnum Peat Moss, Ammonium Sulfate and Acid Fertilizer.
If the aim is raise the pH in your soil you can use: limestone (the amount you use will vary depending on your soil’s needs, so be careful not to use too much, as lime can have adverse effects, like burning the plants), wood ashes etc.
Before applying any soil amendment, have your soil tested to determine the types and amounts of soil amendments required.