You can, over time, modify your wants, so that you no longer want undesireable things, or at least not as much, and learn to want desireable ones. We certainly have the freedom to satisfy our desires or not, e.g. giving up smoking, giving innocent pleasures up for lent, and we can choose between different desires when only one is possible (e.g. do I spend my last fiver on a couple of pints in my local Wetherspoons, or a box of chocolates?).