If this is the mobo it needs BIOS 1.6 on it before it'll support that CPU
Core i5 Haswell Refresh i5-4590 100 3.3 1M 6M C0 84 HD Graphics 4600 1150MHz 7850v16.zip
If this isnt on it then you'll have to take it to a shop and ask them to do it with a cpu it supports
Or you'll have to buy a CPU it supports then do it
Unless it supports something like USB BIOS flashback. Which some ASUS mobos support
Have you got the mobo and / or CPU now??