The date is displayed in four places:
- Posts on the blog/archives
- Individual post pages
The format of the date in all four places is based on your site's date format setting. To change your site's date format setting:
- Visit the Settings menu (Settings → General)
- Locate the Date Format section
- Pick an available format, or create your own format
- Click the Save Changes button
The date format has now been updated across your site.
Note: if you want to create a format, WordPress has detailed documentation on date formatting you can follow.