How can potential energy be increased and decreased?

By changing the object's position.

There are several forms of potential .

1) An object with mass will have potential energy by placing it in a gravitational field (like the gravitational field of the Earth). The potential energy can be increased by a force raising the object to a higher location and decreased by allowing gravity to pull it to a lower location.

2) A charged object will have potential energy when placed in an electric field (which may be generated by another charge). If the charges are alike (both positive or both negative) the potential energy will increase when pushing them closer together and decrease when allowing their repulsive forces to push them farther apart.

3) An object can have potential energy by being compressed or stretched (like a spring). The amount PE can be increased by stretching or compressing the spring more. The PE will decrease when the spring returns to its original length.