Decrypt Membership Hashed password saved in Database

Hi
I have a database of old developer, who left the team, he was using the Asp.net Membership for User Registration and for userLogin.
all password are saved in aspnet_Membership table in Hashed Encrypted format.
I want to change the database structure , so i need to get all user password in plain text.
I applied so many methods for decrypting the password but no success.  my web.config have this configuration.
<add name="AspNetSqlMembershipProvider" type="System.Web.Security.SqlMembershipProvider,System.Web, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a" connectionStringName="MainConnectionString" enablePasswordRetrieval="false" enablePasswordReset="true" requiresQuestionAndAnswer="false" applicationName="ibuy" requiresUniqueEmail="true" passwordFormat="Hashed&qu ...