It sounds like a browser setting, so how you access it would depend on the browser you have. In my (older) Firefox I'd go to Tools > Options > Content > Fonts and colors. Every browser I've looked at seemed to have something similar but not necessarily in the same place.

If the change turns out to extend beyond your browser, you'd want to look for something like My Computer > Control Panel > Display. Again, the way to it might be different with newer versions of Windows than mine.

Good luck, bebop, and let me know how this works for you.