If you want to adjust the date display in your Outlook calendar, the place to make the change is not in Outlook but your Windows control panel.
From the Start menu, select Control Panel. Now click Clock, Language, and Region:
Here you’ll pick Change date, time, or number format:
You can simply select a pre-set from the Long date dropdown list, but you’ll have more control if you click Additional settings:
Click to the Date tab and customize the Long date format to whatever presentation you like:
I prefer having the day appear before the month and use a single "d" so that no zeros are added to dates less than 10. I also changed the month using "MMM" so it is neatly abbreviated to three characters:
Experiment with this setting and see what format works best for you.