When trying to install Big Sur on my 15" MacBook Pro, it tells me that I can't because I need more memory

If upgrading from macOS Sierra or later, macOS Big Sur requires 35.5GB of available storage to

upgrade. If upgrading from an earlier release, macOS Big Sur requires

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.