To increase the font size of netbeans 7.3.1 and 7.3 , you go from menu Tools>>Options>>"Fonts & Colors" (is an inner menu in the dialog window of Options)
At the "Syntax" tab ,every entry in the "Category:" list-box ,you will notice that the font has the value "Inherited". If you find in the "Category" list-box the entry with the name "Default" and change the font value of that, you will affect the font size of your editor, because everything is inherited from "Default" entry .
Another method is to increase temporary the font of the editor by a combination of keys. To find what are the keys go to the "Options" dialog window by Tools>> Options and then choose the "Keymap" menu entry and then in the "Search" textbox type "zoom text" and it will show you what combinations of keys for zooming in /out.
for example mine is the combination of "alt" key + mouse wheel up/down