I cannot update the iOs in my MacBook

iOS only runs on a mobile device.

MacOS Big Sur requirements

From: How to upgrade to macOS Big Sur - Apple Support

"If upgrading from macOS Sierra or later, your Mac

needs 35.5GB of available storage to upgrade. If upgrading from an

earlier release, your Mac needs up to 44.5GB of available storage. To

upgrade from OS X Mountain Lion, first upgrade to OS X El Capitan, then

upgrade to macOS Big Sur."

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

Free up storage space on your Mac

OmniDiskSweeper

See used and available storage space on your Mac

From above link

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.