Example of changing password in AD (from: http://stackoverflow.com/questions/1066131/how-to-programaticly-change-active-directory-password)

PasswordChangeAd.cs

using (var context = new PrincipalContext( ContextType.Domain ))
{
  using (var user = UserPrincipal.FindByIdentity( context, IdentityType.SamAccountName, userName ))
  {
      user.SetPassword( "newpassword" );
      // or
      user.ChangePassword( "oldPassword", "newpassword" );
  }
}

PasswordChangeAd1.cs

// alternative
public void ChangeMyPassword(string domainName, string userName, string currentPassword, string newPassword)
{
    try
    {
        string ldapPath = "LDAP://192.168.1.xx";
        DirectoryEntry directionEntry = new DirectoryEntry(ldapPath, domainName + "\\" + userName, currentPassword);
        if (directionEntry != null)

        {
            DirectorySearcher search = new DirectorySearcher(directionEntry);
            search.Filter = "(SAMAccountName=" + userName + ")";
            SearchResult result = search.FindOne();
            if (result != null)
            {
                DirectoryEntry userEntry = result.GetDirectoryEntry();
                if (userEntry != null)
                {
                    userEntry.Invoke("ChangePassword", new object[] { currentPassword, newPassword });
                    userEntry.CommitChanges();
                }
            }
        }
    }
    catch (Exception ex)
    {
        throw ex;
    }
}