How can air pressure be changed?

Using the equation P1V1/T1 = P2V2/T2 we find there are two variables we might influence in order to change the pressure of a gas. (P=pressure, V=volume, T=temperature in degrees Kelvin) By increasing or decreasing the temperature of the bottle, you can increase or decrease the pressure within. If the bottle is made of a flexible material, like plastic, you can apply pressure to the bottle. By either squeezing the bottle or increasing atmospheric pressure outside, you deform the bottle and decrease it's volume. Since the quantity of gas inside the bottle is constant, the decrease in volume increases the pressure. Likewise to decrease the pressure in a sealed flexible bottle, you can decrease air pressure outside.