How do enlarge a program to fill the screen?
I am going to assume you mean change the shape of the window....
Move and shape windows
Windows are rectangles that open on your desktop when you start a program. A window can fill your entire screen or take just part of it.
There should be three little boxes up on the top right of each window. Starting from the right, an X that when you click, will close the window; a single box or two boxes that if you click will change to the other form; and a dash – that if you click, the window will disappear from view, but still show up on the task bar at the bottom of your screen.
If that 2nd box is a pair of squares, your window takes up your entire screen. The window can not be moved or change shape.
If that 2nd box is a single rectangle, your window is in the form of a shapable, movable rectangle (like the window in your room). If it looks like it still takes up the entire screen, then you need to re-size or re-shape it.
To re-shape a window, move your mouse pointer to any window border. When you have it in just the right spot, the single arrow will change to a two-headed one. If you hold the left button down (assuming your computer is set for a right hander) while that arrow is two-headed, you can drag that window’s border in either direction.
If you move that pointer to a corner, the arrow will take the shape of a two-headed arrow, but be angular. By holding down the left button while dragging, you can re-shape the window in both dimensions at the same time.
Once you have it the right shape, you can move the window. The very top of the window is called the title bar. By left-clicking and holding the arrow on that spot, you can drag the window to where ever you want it to be on your screen.
Windows will remember the shape and position of the window. So, the next time you open that particular window, it will resume the shape and position you last left it in.