Because there is a possibility of data loss, and backing up will prevent this. It is worth doing if you value the files on your computer!
data files
When upgrading and you want to keep files and settings from the previous system, use Migration Assistant. Don't do a clean install, which will erase the first system.
Upgrading a computers operating system will not touch the personal data on the computer. It is always advisable to keep a back up of your data in case of disk failure.
data files
Yes, you should for safety measures. Can use time machine, cloning utility to take back-up of important files.
Sometimes when upgrading the OS of your computer there is a risk of losing the data on your computer even with minor upgrades. it is always suggested to back up the contents of your computer just in case your data did happen to get erased.
Before making any significant changes to your computer, back up your files. That way, if something goes wrong, you can at least recover your data.
Before upgrading the operating system, check the minimum requirements of the new operating system to ensure that the computer meets the minimum specifications required. Check the HCL to ensure that the hardware is compatible with the new operating system. Back up all data before upgrading the operating system in case there is a problem with the installation.
That isn't necessary.You only have to back up the computer you're actually upgrading.
Consider backing up the whole hard drive, or at least the OS (keep all of the OS together as is, don't copy some parts of it and leave others as this will cause problems) and important stuff. If you don't want to back up the OS, back up your important stuff and create a recovery partition, which your computer manufacturer can help you with.
You cannot 'remove' the Mac OS. The computer will not function without it. Macintosh computers need, and can only function with, the Mac OS. What you can do, possibly, is revert to an earlier version of the OS, if you still the disks the computer came with, or you can possibly upgrade to newer OS than the one you are currently using. If you want to revert, then insert the installation disk and set it as the start-up disk and then follow the onscreen instructions. This will delete the existing OS and install the desired one. If you are upgrading, insert the installation disk and set it as the start-up disk. Then follow the instructions. This will upgrade the existing OS to the newer one.
Upgrading to that patch is no longer available. The reason for this is because Windows has just released Windows 10, if you want to upgrade it would need to be to that OS. This can be done in your control panel, there will be an option there.