I received a message indicating that my MacAir does not have enough space to install Big Sur. It is a 2015 MacAir, running MacOS Catalina 10.15.7. It has 8GB memory
Can I install Big Sur?
MacBook Air 13″, macOS 10.15
Question marked as
The issue would be storage, not memory. 8GB is memory.
See the following from How to upgrade to macOS Big Sur - Apple Support
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.
You can view how much storage you have available at Apple menu > About This Mac and then click Storage at the top of that window.
The following may also help: How to free up storage space on your Mac - Apple Support