HCA: Hermit Crab Association

I see them moving around under the substrate but have never seen them above. I have seen the sand and food a mess but that was a few weeks ago.

I currently have a 10 gallon tank, I want to upgrade their tank, how do I go about doing this, do I use the same substrate and add more? The 2 crabs are always buried in their substrate, so I don’t know how to get them out without harming them if they are molting.