Get Hashed password back

Hello,
i am using

System.Web.Security.FormsAuthentication.HashPasswordForStoringInConfigFile(txtPassword.Text, "SHA1");

for converting password in hashed format.
but when i retriewd my password in format like

"84A516841BA77A5B4648DE2CD0DFCB30EA46DBB4"

i need its original form , how to convert it to back ;