Nie wiem jak to zrobić 
Przez ubootenv set boot_part tego nie zrobie, bo obie mam nadpisane.
Znalazłem tylko taką poradę:
ddwrt -> stock: i had to enable ssh, then flash both mtd5 and mtd7 partions with stock flat firmware file, AND erase nvram partition (mtd erase nvram), then power cycle router. i cant completely explain why, but i think the ddwrt nvram values make openwrt or stock firmware hang, and issing the 'reboot' command at the ddwrt command line re-writes nvram. anyway, only by completely getting rid od ddwrt could i get back to stock.
Konkretnie jak tego dokonać? then flash both mtd5 and mtd7 partions with stock flat firmware file
I co to jest "flat firmware"?
A może jest jakiś prostszy sposob?
Dziękuje za pomoc!