Thankfully, there are a couple of solutions out there for you if you have discovered that a portrait photograph has not really come out the way that you wanted it to.
For a start, you can first try to use free image editing services which are available online, such as fotor, or Picasa. Although it can often be very tricky to use them, these programmes can give only a slight improvement – but sadly in most cases the changes that can be made look very unnatural and it is all too obvious that someone has tried to alter them!
On the other hand, you could always get the help of freelancers. They will have access to better software (Lightroom, Photoshop), and will be able to use them . . . but there will often be a hidden clause that they will be able to use that image for themselves afterwards. That means that you will lose absolutely all of your privacy, and they could even earn from your images!