Hello. My name is, Mike. If by browser windows, you are referring to the Internet browser you are using (e.g. Internet Explorer, Firefox, etc.) the issue is with the view settings of the browser. This can easily be adjusted. Simply press the left mouse pad button, then using two fingers on your your mouse pad and pinch them together. This will reduce the size. You can also hook up an external USB mouse and do they by left clicking on the mouse button and using the roller ball on the top of the mouse by rolling it toward you to reduce the size. Lastly you can do this by going into the browser settings and changing the view size.
If by chance you are referring to the size of your Windows desktop then you are dealing with a screen resolution issue. This too can easily be changed by left clicking on the Windows desktop and selecting display settings. From there you can adjust the screen resolution to reduce the size.
You need to clarify if the issue you are experiencing is in the web browser only or withing the OS. Please refer to the following: