Cannot download Big Sur installer

I am unable to install Big Sur operating system on my late 2015 iMac. When I tried update from Software Update download seems normal until 12.1 8GB is reached that it hangs up for two minutes and alerts me that the download has failed. I have tried to download it over two dozen times since it was released on Thursday. I have done a clean install of Catalina, reset the PRAM, trying to update it after starting into Safe Mode, gone into Recovery Mode and run disk utilities all with the same result. What can I do to load this operating system on my computer.