Check the disk space
The first thing you should do is to make sure that there is plenty of free space on the disk drive before you try to download or install Windows 10. Allow 5GB to download the upgrade and at least another 15GB to install it. You should not even consider upgrading unless there is at least 20GB of disk space and preferably more. You need more free disk space if you are running the 64-bit version of Windows.
Open an Explorer window and select This PC or Computer. All the drives are displayed and you can see the used and free space.
Check the disk
Before you start, shouldn’t you check that the disk drive is actually OK? It may contain errors and those errors could be magnified when lots of files are moved around, as they will be when Windows 10 installs.
Open an Explorer window and select This PC or Computer. Right click the C: drive – the boot disk – and select Properties on the menu. Select the Tools tab and then click the Check button in the Error checking section.
In Windows 8, click Scan drive, even if it says you don’t need to. In Windows 7, tick Automatically fix file system errors, and click Start. It will not start, but if you restart Windows the disk will be checked.
Check for compatibility
If your computer is running Windows 8.1, then it should run Windows 10. If it is running Windows 7 or 8, you should run the Windows Upgrade Assistant. Right now, this only checks for Windows 8.1 compatibility, but Microsoft may change this to Windows 10. If it says the PC is fine for 8.1 then it is fine for 10 too, so go ahead and run it.
Back up the system
There is an old saying, ‘Hope for the best, but plan for the worst’. In other words, plan for total disaster. The worst thing that can happen is that part of the way through installing Windows 10, the system freezes, shuts down, will not start and so on. If you cannot boot Windows, what then?
If you have a backup then the system can be put back the way it was. Restore discs that were created when the PC was new are of little use. They remove everything and put the system back the way it was on the day you bought it, probably with Windows 8 and no software and no documents, photos, videos and so on.
You need a full system back, one that can be restored even if the PC will not boot. There are several applications can do this and they write an image of the disk exactly as it is now, to a USB drive. They then provide a boot disc or turn a USB flash memory drive, or thumb drive, into a boot drive. If the PC will not boot, you can boot from the CD or thumb drive and restore the image from the USB disk.
Once all these tasks have been performed, you can install Windows 10. There should not be any problems, but if there are, you are covered.