Gas pressure can be increased either by raising the temperature or by decreasing the volume (if the container is flexible).
Most gases obey the ideal gas law to at least a good approximation:
where n is the number of moles of gas, R is the universal gas constant, T is the temperature in Kelvins, and V is the volume of the container.
If V is in liters, then using R=0.082054 L-atm/(mol-K) gives P in atm.
If V is in cubic meters, then R=8.314 J/(mol-K) gives P in Pa (pascals).