これで動いたよ

Public Class Form1
Public Declare Function SetWindowPos Lib "user32" _
(ByVal hwnd As Integer, ByVal hWndInsertAfter As Integer, _
ByVal X As Integer, ByVal Y As Integer, _
ByVal cx As Integer, ByVal cy As Integer, _
ByVal wFlags As UInteger) As Boolean


Private Sub Button1_Click_1(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
SetWindowPos(Me.Handle, -1, 100, 100, 500, 500, &H40)
End Sub
End Class