000RICO000                                                                                     

This machine will run Windows 8.1 64 Bit fine, the problem is the Microsoft Windows 8.1 Media Creation Tool won't run on Windows Vista. You need to run it on Windows 7, 8, 8.1 or 10 so it'll be best to buy Windows 8.1 as a retail package opposed to a Digital Download.

Once you have the DVD use it following the instructions here:

http://dellwindowsreinstallationguide.com/a-clean-install-of-windows/windows-8-1-installation/

These drivers will work for Windows 8.1:

http://dellwindowsreinstallationguide.com/driver-sets/inspiron-desktops/inspiron-531-windows-7-64-bit/