These are the steps I use. There are probably others that work just as well, or better.
1. Make sure LaunchBox is not running.
2. Start RetroArch manually and go to Online Updater/Core Downloader, select the SNES 2010 core and hit Enter
3. Exit RetroArch and start LaunchBox and goto Tools/Manage Emulators, scroll down and select RetroArch, then Edit. Select Associated Platforms, then scroll down to Super Nintendo Entertainment System, select the drop-down in the Core column and select the snes9x2010_libretro entry. Select OK. If prompted to update all SNES games to use this emulator, select Yes.
4. Run a SNES game and see if you see anything different.