AR-750ac post 3.201 update+LuCi =no storage space left

I was using my Neon (linux) desktop browser to access webadmin panel, updated fw from within gui. I then thought install luci… Did successfully but unsuccessful in login to luci in gui,
I attempted to install file server plugin and it said it had no space available.
It was at 3% remaining prior to luci install! Obviously the 3.201 update was very big!
I thought :ok_hand: I put mSD (tf) card in and it will use that memory as idk swap? Then I realized no this is onboard ROM, fixed capacity. So I don’t see how to uninstall (or how to login to luci on 1st use!)
Am I supposed to access luci by terminal client?
Who is root ? I thought it was me?
What secrets does it want affirmed or presented?

I just want to go back now so I can incrementally add to its configuration. Id like to know how to unf*#! my new router so I can be at :v: