Replace multiple hyperlinks

I think maybe the drive would be T:\ not T:\\ so you need:

Sub ChangeHyperlinks()
Dim h As Hyperlink
Dim oldDr As String, newDr As String

oldDr = "T:\servername\"
newDr = "http:\\webaddress\"
For Each h In Sheets("Sheet1").Hyperlinks
h.Address = replace(h.address,oldDr,newDr)
Next h
End Sub