if its chrome, just click on the wrench and go to settings and you should see a zoom + and - sign. hope that helps. if not please tell us the browser you are using. Since all browsers are different to access the settings menu
In Firefox go to the menu on top and click "View". Move the mouse over "Zoom", then click "Reset" when it appears.
In Internet Explorer go to the top right of the screen. There will be 3 icons. One of which looks like a gear and when you move the mouse over it, it will state "Tools". Click it, then go to "Zoom", then select 100% to reset to the default view.