Q: How to exchange iPod touch 5th Gen to iPod 6th Gen

They dont' exchange. If you take in your 5 you will get a small amount of money for it. You will possibly get more if you simply sell your 5. You can also explore places like Best Buy, gazelle and others that buy older devices. I think I got $57 for my 5 when I traded it in at Best Buy (it was a 32 gig is like new condition)

The only trade in that is going on is iPhone 6 for iPhone 7 (with various conditions)

No since Apple has not said anything and the terms of use of this forum prevents speculating about unannounced products