Secret Keys control the funds sent to individual Stacks addresses. Secret Keys are either a 24 word secret phrase that users are prompted to record in the process of generating the Hiro Wallet, or Secret Key connected to a hardware wallet device. A full overview and background on Secret Keys is available here. Without a Secret Key, users cannot access the wallet.
A Password within the Hiro Wallet simply acts as another layer of security that is device-specific. Passwords are created by users and they must meet security requirements. Passwords are useful if you use the same device and same browser every time you use the Hiro Wallet, as it saves you from having to re-enter your Secret Key each time you login. Unlike Secret Keys, Passwords are able to be reset and recovered.
To reset the password, simply log out of the Wallet. You can do this by navigating to the three dots in the upper right hand corner of the Wallet and selecting "sign out." When you log back in, you will be automatically prompted to create a new password.