If you mean without changing anything else except the font size of the icon text, then the only way I know of is via a jailbreak tweak like "Shrink". Have a look at our hacking section for more details on jailbreaking, starting with all our sticky threads in there which should answer your questions about it.
Without jailbreaking, you can use the accessibility features of the iPad in Settings > General > Accessibility > Zoom, but this increases the magnification of the whole springboard, not just the font size.
Attached is a pic using shrink at 150% label size
Hope that helps.