Click on "Modify image size" and choose a new number, not more than 1000.
Every program should have settings that the user prefers and would like to use each time they load the program - Lunar Calculator is no exception. This chapter of the help file lists those items that are configurable.
When you exit the program, you will be asked if you want to save changes to the configuration and/or settings. If any of the parameters below (or those in the Settings window) have changed, you will be prompted.
I won't mention those items that are directly configurable under the Settings menu, since they are covered there, and are more obvious.
By grabbing a corner of the Lunar Calculator window, you can make it bigger or smaller, as well as maximize it to cover the whole screen. Please note that any time you do this, you should re-calculate the image (the button should turn yellow to remind you of this). You can also create a large (up to 1000x1000 pixel) image,through the edit menu:
Click on "Modify image size" and choose a new number, not more than 1000.
See the "zoom" section for details.
You can choose the value for the “magnifying glass” 
and 
(on the toolbar at the top of the image; default 3.5x) as well as the custom zoom in/out panel and drop down selection:
Another "Zoom To" preference that's saved in the configuration file:
Crater labels can be on/off; saved on exit if you say yes. Display angles in deg/min/sec or decimal degrees. If you want to have a dynamic shadow calculation with the USGS texture map, have this checked on.
Most users will want this item checked on. This way you don't have to worry about changes from daylight to standard time. However if you are using Lunar Calculator to simulate views from distant locations you do not want to use the current PC timezone, but the one appropriate for the location.
You can have a preferred directory for exporting images that is independent of the Lunar Calculator directory. The preferred type of image JPG, GIF, BMP, TIF, PCX is also saved.
To change the these settings, enter the values you want directly in the boxes, and on exiting the program, save the configuration.
You must be in the crescent search window:
The values that you enter here, Solar altitude, Maximum age, and minimum lunar altitude, will be saved in the configuration file when you exit Lunar Calculator.