Will the volume of a gas increase, decrease, or remain the same temperature is increased and the pressure is if the decreased?
Both of the effects you mention in the question lead to an increase in the volume of a gas - decrease in pressure and increase in temperature.
We now from Boyle's law - one of the oldest known mathematical relations in all of Chemistry - that pressure and volume are inversely proportional. This means that if we reduce the pressure on a gas sample by a factor of two (half the initial pressure), the volume of the gas will double.
Also, Charles' law tells us that volume and temperature are directly proportional, as long as the temperature scale used is the Kelvin scale. So, doubling the Kelvin temperature will double the volume of a gas.
If we make both changes - double the Kelvin temperature and halve the pressure - the volume will increase by a factor of four.