To increase or decrease the screen image, just press the control button and simultaneously press the plus (+) or minus (-) buttons to increase or decrease the image size.
If you have a mouse with a scroll button you can increase/decrease the size of your screen image or text, by pressing Control and using the scroll button to increase or decrease size.
You should be able to get a full screen (without all the toolbars etc) on any Windows computer by selecting function key F11. You can return to the normal screen again by just pressing F11.