Follow the previous advises - First
Though, I would be carful about " I'm using 835 GB of 1 TB storage " even if not upGrading and even more so if UpGrading
It is generally a good computer practice to alway keep at least 20% to 25% of the Total Drive Capacity’s as Empty Space.
Allowing the computer to drop below these guidelines may eventually, cause unintended consequences.
If upGrading to newer version of macOS >>
Suggest having at least 50 GB of Empty Space on the drive.
It will allow the Full Version ( about 12.xx GB ) to download, expand and then commence to install.
Lack of empty space when upGrading could result in great disappointments or worse still ,failed upgrade
Part 1 of 2
If still having issues >>>
There are factors:
1 - Like poor Wifi connection
2 - Slow wifi connection
3 - Too many other people downloading at the same time and Apple Severs are overloaded
4 - Software on the computer interfering with the download process including AntiVirus Software
Notation: Disabling the AV Software may or may not solve the issue. Removal of the AV Software may increase the chances of the download to perform as expected.
5 - Running behind a VPN which may increase Packet losses or corruption of the download
6 - If via wifi too many Other devices using the wifi at the same time reducing the Bandwidth to your computer.
7 - Best Results are via Ethernet Cable to Router
Should you reach macOS 11 Big Sur there is a separate update for Safari to version 16.6.1
Should you reach macOS 12 Monterey or macOS 13 Ventura there is a separate update for Safari 17