Hello @kamild1996, I used openwrt-ar71xx-generic-wnr1000v2-squashfs-factory-barrier-breaker-r44095-img as described in my post and the linked post there which describes exactly what I did. It's a while since I did it so it has left my main memory 
but it did work for me.
That said, the WN604 is very low-spec and can only just accommodate the firmware. As soon as I tried to install anything else I hit resource issues and problems. So don't expect much more that what it comes with. But that is infinitely better than the Netgear firmware