From Silicon Investors
It varies by system. Try the following methods:
If you have a mouse with a scroll wheel, hold down the CTRL key while turning the mouse wheel. On a touchpad, hold the CTRL key while dragging your finger along the right edge of the touchpad.
While holding the CTRL key, press "+" to increase the font size, and "-" to decrease it.
In IE, select View-->Font Size. Keyboard alternative: Alt-V-->X-->Letter for desired size.