How to remove from D-Link DIR-869 LEDE firmware to stock firmware?

Hello Evereybody!
I have installed this firmware "lede-17.01.4-ar71xx-generic-dir-869-a1-squashfs-factory.bin" to my router.
The firmware is working on the router, but I don't understanding for the linux operation system.
I need to remove this firmware, because i'm stupid for this "router editing, settings language".

Please tell me, how can I remove this firmware edition.
I've found a similar topic whit this problem: Need major help with going back to OEM firmware [Solved]

I was downloaded and installed winscp software, but not connected with the router, by user and password error.
I searched in in the lede pade, where is the sysupgrade, where is the terminal, but not found.

Please tell me step by step how to describe how and what to do to restore dd-wrt or factory firmware.
Thanks in advice