Both are correct. You can use "things" all by itself or after any of a large number of determiners: the things some (or 'all') things some (or 'all') of the things these things my (or 'his', 'your', etc.) things such things certain things various things "Make things new" is a phrase whose interpretation is wide open. It could substitute for any of the above choices but its meaning is less specific.

Make things new" is the correct phrase. The word "the" is unnecessary and makes the phrase sound awkward.