Please make changes in your aspx.vb page as follow :
Protected Sub ItemCommand(source As Object, e As System.Web.UI.WebControls.DataListCommandEventArgs) Handles DataList1.ItemCommand
Dim myListItem As DataListItem = e.Item
Dim l As ImageButton = myListItem.FindControl("ImageButton2")
Dim img As Image = myListItem.FindControl("Image1")
If e.CommandName = "ImageButton2" Then
img.ImageUrl = l.ImageUrl
End If
End Sub