Mac storage basics · Apps and macOS itself
Can I delete an old "Install macOS" app from my Applications folder?
Short answer: Yes — it's only a downloaded installer and isn't needed after upgrading. Delete it, or keep it on an external drive if you'll make a bootable installer.
Yes. An Install macOS … app is just a downloaded installer; once the upgrade is done (or if you decided not to upgrade) it isn't needed and can be moved to the Trash. They're typically more than ten gigabytes.
Keep one only if you plan to make a bootable installer or reinstall that version, and consider storing it on an external drive instead.