Modern macOS protects iTunes as a system app. If you are on an older OS looking to downgrade: Open the Terminal application. Execute the command: cd /Applications/
Installing an old version isn't always "plug and play." Here are the steps to ensure it works correctly: old itunes download
Downloading old iTunes is relatively straightforward. Here are the steps: Modern macOS protects iTunes as a system app
If you want the lightweight feel of old iTunes but need modern security, consider modern media players built by the community: old itunes download