In Windows, using both Internet Explorer and Firefox, you can choose the View menu, Text Size option to change text size. (The keyboard shortcut is Alt-V, X). Other browsers are likely to have the same or similar options.
To zoom in and out on the entire page, not just the text, hold down the Ctrl key and use the plus (+) and minus (-) keys, or rotate the mouse wheel if you have one on your mouse.
We have not implemented onscreen plus and minus buttons for resizing text on our Web pages because these can interfere with the use of the plus (+) and minus (-) keys described here, which, once learned, are easier to use and work on many more sites.
For the Macintosh, use the Cmd key and + or - to quickly change the font size.