Read the readme for further details.
Beginning with v8.4.0 Update 1, the EnergyPlus installers include a limited set of transition programs. This archive contains transition programs from v8.4.0 to v9.0.0.
Extract the files to /Applications/EnergyPlus-n-n-n/PreProcess/IDFVersionUpdater/
If any files are duplicates, you may allow these to overwrite. These are 64-bit binaries.