Big Sur Download - not enough space on HD

It told me I need 12 GB to download it, so I spent two hours clearing up space. It took another two hours to download the installer. Then, when I went to install it, it said that I needed to clear up another 35 GB on my HD!!!! WTH? I had a hard enough time clearing the original 12 GB. Does anyone know of a way around this? I've seen responses mentioning doing it on an external HD, but I'm not that tech-savvy. Help!