To change your pin via the app:
Go to "Settings".
Click on "Security Settings".
Click on "Change Pin".
Enter your current pin and the new pin in the designated fields.
Click on "Change Pin" to successfully change your pin.
To change your pin via the website, click on the blue profile icon at the top-right side of the page.
Click on "My profile".
Click on "Pin".
Then follow the prompts mentioned above for the app.