VB: Deleting a key value when there is an array of values for a key?

I'm trying, with no success, to find and delete a value associated to a key when a key may contain more than one value. For example, when I built the key I did this:

        If oKey.ContainsKey(ListBox2.SelectedItem) Then
            oKey(ListBox2.SelectedItem).Add(ListBox1.SelectedItem)
        Else
            oKey.Add(ListBox2.SelectedItem, New List(Of String))
            oKey(ListBox2.SelectedItem).Add(ListBox1.SelectedItem)
        End If

So I may have something like this:

Key               |       Values

Folder1         |        File1, File2, File3

Folder2         |        File1

Folder3         |        File1, File2

I want to be able to delete the File2 from Folder1. Would anyone be able to jump start me in the right direction?

SV