oxnas(OX820)/Medion from openWRT to debian (2 replies)

Hi,
I have set up openWRT on my oxnas according to these instructions. Serial connection is available.
Unfortunately the Samba performance is very bad (~10MB/s).

Now I would like to try Debian.
Due to lack of Linux experience/English knowledge I would need a little support. Which of the instructions in the forum can I use to get from openWRT to debian?

uBoot:
I would like to update the uBoot for easy USB boot.
https://forum.doozan.com/read.php?3,16017 <-- This is the right one for me? If I understand correctly the uBoot is replaced in the NAND. Is this the base system I can abort on boot?

will the entries be replaced or supplemented?

root@ChrisNAS:~# cat /etc/fw_env.config change no Problem
/dev/mtd2 0x0 0x20000 0x20000 1
root@ChrisNAS:~# cat /proc/mtd could not write with nano
dev:    size   erasesize  name
mtd0: 00040000 00020000 "stage1"
mtd1: 00380000 00020000 "u-boot"
mtd2: 00080000 00020000 "u-boot-env"
mtd3: 009c0000 00020000 "kernel"
mtd4: 07200000 00020000 "ubi"

Debian:
How is Debian installed. USB stick or can that also be in the NAND like openWRT?
Debian: https://forum.doozan.com/read.php?2,16044 <-- am I in the right place?

Can someone explain me roughly step by step how to get from openWRT to Debian?

Thanks a lot
Chris