SubD divides the mesh into more surfaces, giving you a smoother, more detailed render. It's a requirement if you want to use the HD characters to their full potential. The downside is that it creates more polys and eats up more resources.
To change it, select your character, open the parameters tab, select the all group and scroll down to the Render SubD Level slider. I usually set mine to 4, which divides the polys in the model 4 times.
Your 2nd render looks good too. Elianeck's lights make a world of difference compared to the stock ones.