WinSCP can protect stored passwords by strong AES cipher. In order to protect such sensitive information you need to set a master password. When a master password is not set, stored passwords can be easily decrypted by malicious software that has infiltrated your computer.
If you set the master password, each new instance of WinSCP will ask you to enter the master password the first time it needs to access protected passwords or to protect a new password.
You can change or remove the master password again later. If you remove the master password, all of the passwords will not be protected anymore.
You can set the master password in preferences.
When you forget your master password, there is no way to recover it, nor the protected passwords.
You can at least reset WinSCP back to unprotected state. Naturally, you lose all the protected passwords.
To reset master password, remove
Configuration\Security configuration section/key.
You also need to remove all protected passwords. For this, search for and remove all
TunnelPassword values from configuration subsections/subkeys of
Sessions section/key. Alternatively, if you are going to set a new master password: While doing that WinSCP will prompt you for previous master password once for every lost password. Just cancel those prompts with