In a world of decline curves, lots of things decrease. Sometimes the word is overused, so using synonyms might be a good idea, keeping in mind the subtle differences inherent in those words.
Decrease suggests a progressive decline in size, number, amount, or intensity.
Lessen means to reduce the amount, rather than the number (countable items), as in to lessen the concentration.
Lower means to move downward, to descend, or to reduce the height or altitude of something.
Reduce means to make smaller, narrower, or shorter, or to downgrade.
Abate means to reduce from an excessive or oppressive value, as in noise abatement.
Dwindle suggests visible reduction to very small amounts or values.
By using the right word for the concept of decreasing, your writing will provide the right nuances and flavor to your readers.