When you first bring up a script's window for editing, the window is initially "selected". You'll see 8 small, boxes along the window's borders. These are "sizing boxes" which you can use to change the window's size. If you move the mouse over one of these sizing boxes, then the mouse pointer will change to a directional arrow to show you in which direction(s) you can size the window. In the picture below, the mouse has been moved over the sizing box in the upper left corner of the window. Red arrows show you where the other 7 sizing boxes are located, although they appear only in the picture below. You will not actually see those red arrows in the Resource Editor. But if you look, you'll see the 8 sizing boxes.

Whenever you see these 8 sizing boxes on the window's borders, then the window itself (as opposed to any control inside it) is selected, and can be resized. If you do not see the 8 sizing boxes on the window itself, then you can select the window by moving the mouse over the title bar (or some blank area of the window), and clicking the left mouse button.

You'll notice that certain size boxes let you size either the window's height or its width, but not both. The size boxes in the window's corners can size both height and width simultaneously.

The location (X and Y position), width, and height of your window is displayed in the status bar. The width and height are measured in dialog units (DLUs), rather than pixels. Dialog units are proportional to the font that you use in a given window. When you change to a different size font for the window, the window's size may change. The purpose of this is so that your window (and the controls inside it) will be automatically sized to accomodate various screen resolutions. For example, you may see the following four numbers appear in the status bar:

4, 18, 160, 100
This means that your window is at an X position of 4, a Y position of 18, and has a width of 160 DLUs and a height of 100 DLUs.