[Haskell-cafe] downgrading GHC version on a Mac

I'm on a MacBook Pro. I'm not very familiar with software installation. Up until now I've been using Stack for GHC work, and it seems to take care of having the right version of GHC. Now I'm going to use GHCJS, and I need to have a system GHC installed (I believe). At some point in the past I installed the Haskell Platform for Mac, and I have GHC 8.01. But I want to downgrade that to 7.10 so that I don't have to worry about compatibility with GHCJS. How do I go about uninstalling GHC 8 and installing 7.10 in its place? Can I use Homebrew? D