If you forget your password, ask the system administrator (root user) to assign a new password to your account. Only root can do this.
In general, no one can retrieve your old password from the /etc/shadow file. If your password is short or a single word, your system administrator—or a hacker—can easily figure it out, but you're better off with a new password.
If you're the system administrator, and you've forgotten the password for root, you need to find an alternate way to access the /etc/passwd and /etc/shadow files in order to reset the root password. Some possible ways to do this are: