How to release picture from picturebox so picture file may be deleted in VB.NET

I have a picture box ThePic on the form PicViewer that is assigned an image using the below code from an array of possible picture names (FileNameSt) stored in PicList where CurNum is the array position of the file name:

Private Sub LoadPic(ByVal FileNameSt As String)
    Me.ThePic.Load(PixFolderPath & "/" & FileNameSt)
End Sub

Once the user has loaded the picture into the form, they have the option to delete the picture from the file. The code I am trying to do this with is as follows:

 Private Sub DelButton_Click(sender As System.Object, e As System.EventArgs) Handles DelButton.Click

    Dim Resetter As Boolean
    Resetter = False

    If Not PixLoaded Then Exit Sub 'User has not selected a file to load pics from
    If UBound(PicList) = LBound(PicList) Then PixLoaded = False 'Last pic was deleted
    Me.ThePic.Image = Nothing
    Me.ThePic.Invalidate()
    Me.ThePic.Refresh()
    If Not PixLoaded Then
        Me.ThePic.Image = My.Resources.NoMorePics 'Out of pics picture
        Me.ThePic.Refresh()
        GoTo Finisher
    End If

    'Go to the next image available
    If CurNum = UBound(PicList) Then
        LoadPic(PicList(LBound(PicList)))
        Resetter = True
    Else
        LoadPic(PicList(CurNum + 1))
    End If

 Finisher:
    My.Computer.FileSystem.DeleteFile(PixFolder & "/" & PicList(CurNum))

    If Not PixLoaded Then Exit Sub 'Exits if on last pic

    LoadPictures(PixFolder) 'Resets PicList array values 
    If Resetter Then CurNum = LBound(PicList)
End Sub

My issue comes when the user is trying to delete the last picture out of the file. For some reason I get the "The process cannot access the file 'File Name Here' because it is being used by another process." error on My.Computer.FileSystem.DeleteFile(PixFolder & "/" & PicList(CurNum)). How do I remove the picture file from being used by my form so it can actually be deleted?