Hi dabeers,
Welcome to the Mattress Forum! 
The return/exchange policies for Dreamfoam depend on the mattress. Some of their mattresses have comfort layers that can be exchanged for a different firmness level (see post #7 here). If the mattress you purchase is fulfilled by Amazon it would be subject to the Amazon large items return policy and if it’s fulfilled by Dreamfoam then they generally doesn’t allow returns or if they do they would be through a more costly common carrier because the mattresses can’t be re-compressed.
Phoenix