**NOTE**
In addition to the information at the link above, it is recommended that you disable both Secure Boot and Fast Boot in the BIOS/UEFI settings as some systems may not support booting from USB or Flash drives with them enabled. Also, as a measure of protection against a failed installation, all of the following are highly recommended prior to beginning the clean install process.
1. Check that the software and hardware you mostly use are comptible with Windows 8.1 or 10 and have drivers available, even if your system has already passed the compatibility check. Download and save these drivers to a suitable DVD, flash drive or external disk so that in the event you need to install them later, you can do so without needing to go find them when it's no longer convenient.
2. Create a backup of any important files and folders to an external source or cloud service. Better yet would be to additionally or alternatively create an entire system backup image using a utility like Acronis True Image or Macrium Reflect so you can simply restore your previous installation to it's exact self if something goes wrong or doesn't work out later on.
3. If your only installation media for your current or previous operating system is a factory recovery partition, it might be a good idea to also copy THAT image to another location as well. External or secondary drives would be good choices as locations to save these types of images.
4. Before you begin the installation process, it might also be a good idea to ensure that your BIOS is set to UEFI or compatibility mode. Legacy modes that may have worked fine with Windows 7 may create installation or hardware issues during or after the installation of Windows 8.1 or 10.
5. Temporarily disconnect ALL other hard drives except the primary drive that windows will be installed to. With the power turned off, simply disconnect ALL other internal drives from the motherboard SATA headers or external drives from their USB ports, except the flash drive or optical drive to be used DURING the installation process. This step will prevent the possibility of accidentally deleting any files or partitions from those drives when preparing the primary drive for the Windows installation.
6. If you have partitions on the hard drive that will be used for the new operating system which are being used for other, Non-OS purposes, then back up any information on there to another location as we will be completely removing all existing partitions from the target drive. Do not forget this step as any existing partition information on the drive will be eradicated during this process.