"pimple" is a good solver to work with, as it handles transient cases with RAS or LES turbulence. To change turbulence models, you'll need to specify this in your "turbulenceProperties" file by changing "simulationType" from "RASModel;" to "LESModel;" and providing an appropriate "lesProperties"file.
I'd suggest checking out the channel395 tutorial in tutorials\incompressible\pimpleFoam to see the usage of LES turbulence models. You'll also need the same boundary conditions for the solver (such as nuSgs, nuTilda, etc.)
That should be about it, and if you're missing something the error should point you toward something else to copy/modify.
For grid refinement, you'll want to have a much finer grid in regions with large gradients, because LES needs a finer resolution to resolve the turbulent kinetic energy accurately. It really depends on your flow conditions though. Try solving with your initial RAS mesh, then refine it in areas with sharp velocity gradients to improve your results.
I don't use "pimpleDyMFoam" for my research, but I am studying turbulent jets using "pimpleFoam" as a solver. pimpleDyM just uses a moving mesh.