Refresh Combo Box after first combo box option changes

Ive got two combo box's, the first one you select the folder, and the second one lists all the folders within that folder for you to select from.

How can I get the second combo to rescan when I change select of the first one?

This is what ive got at the moment, I just need it to update the list if I change my folder selected in the first combo.

$Folder = GUICtrlCreateCombo("C:\Folder1", 142, 122, 435, 22, BitOR($CBS_DROPDOWN,$CBS_AUTOHSCROLL))
GUICtrlSetData(-1, "C:\Folder2")

Local $folderselector = GUICtrlRead($Folder)


If $folderselector = "C:\Folder1" Then
Local $FileList = _FileListToArray("C:\Folder1")
_ArrayDelete($FileList, 0)
$sFileList = _ArrayToString($FileList, "|")
Else
$folderselector = "C:\Folder2" Then
Local $FileList = _FileListToArray("C:\Folder2")
_ArrayDelete($FileList, 0)
$sFileList = _ArrayToString($FileList, "|")

EndIf