After returning the height of the active session window, this example reduces the height by 50%.
Sub Main()
Dim Sys As Object, Sess As Object
Set Sys = CreateObject("EXTRA.System")
' Assumes an open session
Set Sess = Sys.ActiveSession
StartingHeight = Sess.Height
MsgBox "This will shrink the current window by 50% (currenty " + Str$(StartingHeight) + " pixels)."
Sess.Height = Int(StartingHeight/2)
End Sub