Backing up currently installed firmware before install Openwrt (dwr-921, jboot)

I have a Dlink dwr-921 C3:

which came with the stock firmware at 1.0 dated december 2016 which is pretty stable for me. On dlink website the oldest version available is 1.01 dated may 2017. I was wondering if is there any way I can backup or dump the currently installed firmware in any way, through JBOOT or otherwise before proceeding with installing openwrt, as I've read newer firmware is more problematic (for some the other way around, not for me though). Thanks