liquify is a great tool, but it's best for fine tuning a layer, rather than for doing the actual enlarging.
i'd recommend enlarging with Edit: Free Transform to get the size correct, then use liquify for shape, then the eraser tool with a hard edge to trim the edges to a nice sharp smooth line.
then you usually need to do some shadow work, to make the lighting of the boobs more believable. subtle is best, but it needs to be in keeping with other shadow intensities in the picture. the burn tool is great for shadows.
use lots of layers if you need to, and to experiment with different approaches.
