Think this is what your trying to do
#include "GUIConstants.au3"
$title = "My GUI UpDown"
GUICreate($title,-1,-1,-1,-1, $WS_SIZEBOX)
$input = GUICtrlCreateInput ("2",10,10, 50, 20, $ES_NUMBER)
$updown = GUICtrlCreateUpdown($input)
GUICtrlSetLimit($updown,100,0)
$old = 2
; Attempt to resize input control
GUICtrlSetPos($input, 10,10, 100, 40 )
GUISetState ()
; Run the GUI until the dialog is closed
While 1
$msg = GUIGetMsg()
If $old <> Int(GUICtrlRead($input)) Then
If $old < Int(GUICtrlRead($input)) Then; up
$old = ((Int(GUICtrlRead($input)) - $old) * 5) + $old
If $old > 100 Then $old = 100
GUICtrlSetData($input,$old)
Else
$old = (($old - Int(GUICtrlRead($input))) * -5) + $old
If $old < 0 Then $old = 0
GUICtrlSetData($input,$old)
EndIf
EndIf
If $msg = $GUI_EVENT_CLOSE Then ExitLoop
Wend
msgbox(0,"Updown",GUICtrlRead($input))