Editing telephone number in active directory from VB.NET

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VB

SharePoint

Dear brothers & Friends,
I am not very much expert in writing fields in active directory I really need your help please.
I am able to retrieve user information from Active Directory as per below code. but how can I authorized current to edit and update there telephone numbers. this application is running in sharepoint server.

Dim netBIOSname As String = Me.Page.User.Identity.Name
      Dim sAMAccountName As String = netBIOSname.Substring(netBIOSname.LastIndexOf("\"c) + 1)
      txtuser.Text = sAMAccountName
      Try
          Dim userName As String = txtuser.Text
          Dim searcher As New DirectoryServices.DirectorySearcher( _
             "(mailNickname=" + userName + ")")
          Dim result As DirectoryServices.SearchResult = searcher.FindOne()
          If result Is Nothing Then
              Label2.Text = "Unable to find user: " + userName
          Else
              Dim employee As DirectoryServices.DirectoryEntry = result.GetDirectoryEntry()
              txtfirstname.Text = employee.Properties("givenName").Value.ToString()
              txtlastname.Text = employee.Properties("sn").Value.ToString()
              txtfullname.Text = employee.Properties("cn").Value.ToString()
              txtempid.Text = employee.Properties("physicalDeliveryOfficeName").Value.ToString()
              txttitle.Text = employee.Properties("title").Value.ToString()
              txttele.Text = employee.Properties("telephoneNumber").Value.ToString()
              txtdept.Text = employee.Properties("department").Value.ToString()
              txtmobile.Text = employee.Properties("mobile").Value.ToString()
              Dim ManagerName As String = employee.Properties("manager").Value.ToString()
              ManagerName = ManagerName.Substring(3, ManagerName.IndexOf(",") - 3)
              Dim searchMgr As New DirectoryServices.DirectorySearcher("(cn=" + ManagerName + ")")
              Dim resultMgr As DirectoryServices.SearchResult = searchMgr.FindOne()

              If resultMgr Is Nothing Then
                  Label2.Text = "Unable to find Manager: " + ManagerName
              Else
                  Dim empManager As DirectoryServices.DirectoryEntry = resultMgr.GetDirectoryEntry()
                  searchMgr.Dispose()
                  resultMgr = Nothing
                  empManager.Close()
              End If
              searcher.Dispose()
              result = Nothing
              employee.Close()
          End If


      Catch ex As Exception
          Label2.Text = "The following error occurred: " + ex.Message.ToString()
      End Try

What I have tried:

retrieve user information from Active Directory