How To Merge Two Datatable

I need to marge two datatable with condition. i table data come from local XML Database and another data come from remote sql data if any update made at remote datatable and then marge with local datatable. i wrote a code below :

Public Sub MargeTwoTable()
Dim SQL As String = ""
Dim RemoteTable As New DataTable
Dim LocalTable As DataTable

[code]....

as you see in my code data come from remote database which update date getter then local database . Both table are same and "ID" is primary key. I code is working well. But problem is that when data more then 1000 updated record so this function take too long in loops.

i write a code like : Dim mm() As DataRow = LocalTable.Select("ID = '" & RemoteTable.Rows(i).Item("ID") & "'"). for finding local datatable id row so when data is more then 1000 it take too long because localtable record more than 100000 records. So I need someone help to modify my code what the best way to write the code.