In order to change the PIN/passcode associated with your Empower account (not your debit card PIN), you can navigate to the Profile section of the app and scroll down until you see an option labeled "Reset App PIN". Once you give that a tap, you will be prompted to enter your current PIN/passcode. Once you've done so, you can enter and confirm your new code.
NOTE: Your Empower PIN/passcode is important. Make sure that it's something that you can remember. If you're prompted for your PIN/passcode and are unable to correctly enter it, you may be locked account of your account. In this case, you'll have to contact empower support at email@example.com to regain access to your account.