Big Sur 11.2.3 won't download (Mac)

Hi folks - I'm a new and very inexperienced Mac user (only since xmas) and I can't get Big Sur 11.2.3 to download. Ive tried resetting the router and plugged in an ethernet so its not a network connection problem and however many times Ive tried I still get the "An error occurred while downloading the selected updates. Please check your internet connection and try again" message, ITS DRIVING ME NUTS!! Can anyone help me?

I'd be extremely grateful for any assistance.

Many thanks

Simon