The LARCH screen size is 640 x 480 pixels which was a full-size display in the old days of 13" monitors. With today's higher screen resolutions, the LARCH window can seem too small. To make the LARCH screen appear bigger you can lower the resolution of the display as follows:
Right-click the desktop and choose Properties. When the window opens, click the Settings tab. Move the slider to select a smaller size such as 1024 x 768, click Apply and accept the resolution. You may want to try several different settings to find the one that suits you best. Some settings will look good and some will distort the image if your display is "wide screen." Find one that makes circles look round, not elliptical.
What you have done is to make your screen size fewer pixels high and wide, thus making the LARCH window take up a larger proportion of the screen "real estate." Remember, to change the resolution back if you find the new setting too low for your other programs.