The first day of the week, as shown in pop-up calendars used to select transaction dates, due dates, and so forth, can be chosen to match the usual practice at your location or your personal preference.
In the Settings tab, click the Date & Number Format link:
From the dropdown box that appears, choose your format:
Click Update to save the change. Pop-up calendars will now display in the new format:
First day of the week formats apply only to the business where they are selected in Manager. In some previous versions of the program, they were set globally for all businesses created. After updating to a version with local settings, you may need to visit Settings to make a new selection.