Upgrading to macOS Monterey - lack of memory

What is “Other” storage on a Mac, and how can I clean it out?

Free up storage space on your Mac

OmniDiskSweeper Safe to use

How to delete Time Machine snapshots on your Mac

See used and available storage space on your Mac

The final word from Apple on Managing the " Other " Category

• Other: Contains files that don’t fall into the categories listed here. This category primarily includes files and data used by the system, such as log files, caches, VM files, and other runtime system resources. Also included are temporary files, fonts, app support files, and plug-ins. You can't manage the contents of this category. The contents are managed by macOS, and the category varies in size depending on the current state of your Mac.

Yes, you can delete the macOS installer which is in the Applications folder.

I think you mean you do not have enough free disk space, about 46GB is required. See the following for making more free space

Free up storage space on your Mac - Apple Support