Many modern apps and browsers have stopped supporting Windows 8.1.
Without security patches, your system is vulnerable to new malware and exploits.
Use a utility like Rufus to burn the ISO to a USB flash drive.
Select your preferred language and choose the 64-bit or 32-bit architecture. 2. Creating Bootable Media
Newer hardware may lack compatible drivers for this OS.
I can also provide a guide on before you perform a clean install.