To access the 'Date Settings', click on Settings (gear icon), then select [System Settings] and scroll to find [Date Settings].

You have the ability to change the format of Short Form dates, and Long Form dates.

Short Form Dates 

The Short Form dates will appear on items like Date Pickers.

Long-Form Dates

The Long Form date will appear on items like Bookings and Quotes.

Once you have chosen the desired format for both the short and long dates click [SUBMIT] to save your choices.