You can't yet, read the FAQ at http://powtoken.com/

Can I sell POW 'lite' for cash?
Not yet. But our plan is to build a 'bridge' between POW 'lite' and POW ERC20 by December 2017. This bridge will allow you to transfer your POW 'lite' onto the Ethereum Blochain where it will becom POW ERC20. You will then be free to sell your POW ERC20 for cash. So, in the long term, the answer to your question is yes.