Modifying a script (rookie) - Delete all files in a folder

How do I set perameters to delete only files from the last 30 days using the
existing script i found on the repository:

 

Hi,

In the article below there is a WSH script (vbscript) by Michael Harris
that deletes files that has not been modified in x days old in a
specific folder and all subfolders.

Newsgroups: microsoft.public.scripting.wsh
Date: 2002-10-07 08:12:33 PST
http://groups.google.co.uk/group/microsoft.public.scripting.wsh/msg/14df6623fc552446?dmode=source

If you want to only delete files that are newer and not older than
the specified number of days,

change
if dtlastmodified < vKillDate then

to
if dtlastmodified > vKillDate then

 

something like what this simple app does:

http://peccatte.karefil.com/software/Purge/DelendaEng.htm