With the Logitech Gaming Software, different configurations can be set and switched with a programmable keystroke: http://support.logitech.com/de_ch/product/g300s-gaming-mouse/downloads#
IMO best all round gaming mouse for lefties. Lots of top buttons, I can't stand side buttons. I've ordered 2 more in stock (which will last me more than 2 years ;))... recommend doing the same as the mouse is already 7 years old.
I'm afraid I have to disagree with you, the DPI is definitely not the most important specs to know.
But to answer your question, the DPI can be changed with the software. The values range from 200-2500 DPI, with a quick Google search you could have answered that yourself ;)