In the bottom right of the browser window, you should see a picture of a magnifying glass, with a percentage next to it and a drop down arrow (an arrow pointing down). Click the arrow and select 100%. You can also try holding the CTRL key and pressing + or - (usually to the right of the zero key).
I'm assuming that you are using Internet Explorer. If you don't know what you are using, it is Internet Explorer. If something else, please let us know.
Cheers