Sorry i thought you were talking about the actual size of the address bar.
If it's the text of the address bar, i think this is a resolution problem, beccause as far as i'm aware, there is no option to increase the size of the address bar
The only thing that it could be is the resolution of the screen size is higher than it used to be. You can change this, but it will make everything on the screen look larger.
1.Try right clicking anywhere on the desktop and go to properties
2.Go to settings
3. On the screen resolution, drag it to the left to either 1024 x 768, or if it's already at this size try 800 x 600
4. click OK
Let me know if that sorts it.