Hi Chinecherem,
Thank you for reaching out with your Total Upkeep questions. From what you’ve described this seems to be a browser based issue rather than one with Total Upkeep. In most cases a Total Upkeep error would be associated with the upload or backup process itself.
With this, it seems your browser will not allow you to download a file this large. You can try changing the setting in your web browser to increase download size or try downloading the backup in a different browser such as Google Chrome which supports up to 6gb downloads out of the box.
I hope this helps!