Exposure describes the amount of light captured. Increasing this value means to increase the value of light coming in - this can be done in several ways, depending on the exposure mode you are in. In P, Av and Tv mode you'll need to change the EV settings to +1 or +2 (or the possible steps in between). Consult your manual for this, usually it's one button and using the dial knob to change this.
In Manual Mode you are free to either lower shutter speed or open aperture.