How to change the date format that shows on the calendar?

To change the date format from DD-MM to MM-DD or vice versa:

Mobile

1. Go to Сalendar Settings
2. in the App Preferences click "Date format"

   

3.  Select the format you like

   

Web-version

1. Go to Account settings
2. In the lower part choose Date format by clicking ⌵ sign