Here's how I did mine, but like I said, I don't think mine is so great. Since you're new to Photoshop , you may need to read-up on each of the steps that I took.
1. Click on Select>Color Range. Use the eyedropper to select the black color of the dress. You'll need to experiment with the 'Fuzziness' slider, but I used a setting of 117.
2. This step is optional, but I went to Select>Modify>Expand and expanded the selection by 1 pixel.
3. With the selection active, press Ctrl+J, which creates a new layer from the selection. The new layer should ideally be only the black dress, but it will also grab anything else that's black in the image. We'll deal with that later.
4. Invert the new layer by clicking on Image>Adjustments>Invert. That changes the black to white.
5. Create either a Curves or Levels adjustment layer and "clip" it to the dress layer, which you can use to further adjust the brightness of the white dress.
6. Add a layer mask to the dress layer and carefully paint with black over any other part of the image (aside from the dress) that was inverted in step 4. This will likely include portions of her hair, the black bracelet, etc.
Edit: Because this particular image is evenly lit, inverting it gave a somewhat acceptable result. But in a different image with different lighting, there may be deep shadows on one side of her body. Inverting that will make dark shadows seem light, and vice-versa, so it throws-off the entire image. Generally speaking, I don't like inverting images to change colors because it usually is not very natural looking. But changing dark to light is fairly difficult and for this particular image I (just barely) got away with it.