If you have a lot of cells to change, you can use a macro to automate it. Paste the following into a new macro, between the "Sub" and "End Sub" lines. Then just highlight all of the cells with hyperlinks in and run the macro. You can customise oldpath and newpath as required.
Dim link As String
Dim cell As Range
Dim oldpath As String
Dim newpath As String
oldpath = "G:\"
newpath = "C:\"
For Each cell In Selection
If (cell.Hyperlinks.Count) > 0 Then
link = cell.Hyperlinks.Item(1).Address
cell.Hyperlinks.Item(1).Address = Replace(link, oldpath, newpath)
End If
Next cell