Installing OpenWrt over DDWRT?

I currently have DDWRT installed on my Netgear R7000. Getting tired of all the issues it has so I thought I would try OpenWRT. Now I'm wondering how I can install it on my router when I already have DDWRT? Or should I flash stock netgear firmware first and then install OpenWRT?

AFAIK as the easiest way for beginners, yes.

the second option

Be aware that there are no usable drivers for BCM4360, so unless you're looking for an essentially wired-only router, this isn't really an option.