What will you check before upgrading machine to higher version of operating system like windows 8?

The RAM and the CPU version.

always check the OS requirements before upgrading.
and that requirements must always comply to your CPU.
in order to avoid PC errors.
but you know what is best, the higher version of OS, the higher upgrade of your computer

The hardware required: Ram- Free space - Vga- CPU

Definitely minimum and recommended system requirements...
after that, any user reported problems with upgrading (loss of data, partitions, etc).
Also, is all hardware and software used by that computer supported by higher Windows version.

CPU, RAM, HDD, Graphcs Card(Optional)

1.
the amount of RAM2.
CPU version3.
VGA4.
Amount of free space on my device

The CPU, Motherboard, and random access memories and video card(optional)

first
1- hardware ability (ram -cpu -vga ..................
2- compability

RAM and hard drive space then vga