Try this first...
With almost all modern browsers you can hold down the Ctrl key on your key board (Command key on a Macintosh) and press the + (plus) key to increase the text size or - (minus) key to reduce the text size.
If that doesn't work...
Click on View menu, Text Size. Choose the Larger or Smaller font sizes until you can easily read the web page.
The Web Accessibility Initiative site provides instructions for other browsers and operating systems.