In my experience the only way would be to buy new. I've tried a number of solutions I found on the Net but none really worked. So I put up with them getting rougher/harder.
As my washer is broken at the moment I've being using my SIL's washer and tumble dryer she has fabrise and such things... awesome! much better than the crusty frozen stuff brought in from our springtime in England.
I can't be the only person to dislike soft and fluffy towels...I like them with a bit of texture. Mind you, I also dislike soft pillows....mine are spelt-filled.