Are you asking whether you can take the burger but not the fries, to quote an example? I don't see why not - but all their meals are priced as such; it's not like BK where you can order a meal package or items separately. I've certainly never seen any prices for deconstructed menus.
If you don't think you'll be able to eat all the food, two of you are allowed to share one, or you could order a child's meal. I very much doubt they'll knock off a couple of dollars if you say 'no fries, thanks'.