I changed my mind on OS Monterey before fully upgrading. How do I remove the 12.3 GB of downloaded files?

I have a MacBook Air Early 2015 and I cleared a lot of space to get OS Monterey. After 30 minutes of downloading 12.3 GB of stuff, it was ready for me to install and then it pops up saying I can't because I still need 11 GB of more space. I don't have anything to delete right now and won't be able to clear any more space. I just want to go back to OS Mojave but I want to recover that 12.3 GB of space to put back my desktop items. How do I do this? Thank you so much.