Maybe this old code will do it for you:
' Macro created 26/10/01 by Doug Robbins to update links in a document
'
Dim alink As Field, linktype As Range, linkfile As Range
Dim linklocation As Range, i As Integer, j As Integer, linkcode As Range
Dim Message, Title, Default, Newfile
Dim counter As Integer
counter = 0
For Each alink In ActiveDocument.Fields
If alink.Type = wdFieldLink Then
Set linkcode = alink.Code
i = InStr(linkcode, Chr(34))
Set linktype = alink.Code
linktype.End = linktype.Start + i
j = InStr(Mid(linkcode, i + 1), Chr(34))
Set linklocation = alink.Code
linklocation.Start = linklocation.Start + i + j - 1
If counter = 0 Then
Set linkfile = alink.Code
linkfile.End = linkfile.Start + i + j - 1
linkfile.Start = linkfile.Start + i
Message = "Enter the modified path and filename following this Format " & linkfile
Title = "Update Link"
Default = linkfile
Newfile = InputBox(Message, Title, Default)
End If
linkcode.Text = linktype & Newfile & linklocation
counter = counter + 1
End If
Next alink
