It would be simpler just to replace 'sample' with 'Sample' in the first cell of each table e.g.
Code:
Sub Macro1()
Dim oTable As Table
Dim oCell As Range
For Each oTable In ActiveDocument.Tables
Set oCell = oTable.Cell(1, 1).Range
oCell.Text = Replace(oCell.Text, "sample", "Sample")
Next oTable
Set oCell = Nothing
Set oTable = Nothing
End Sub