How to switch booting from flash without TV and remote

I ve got octagon mini with inop hdmi and remote, but fully funkcional, defined image from slot2 booted and I would like to change boot from flash. Iam booted from slot2 now and I wanted to update oct-define image, but no more webcontrol after doing that. Is there any telnet command, how to flash from boot /or any other procedure/? Im not able to flash from usb, because no remote, or picture for selection in menu-usb flash. Thank you for yout time and help

All, what i can get is webinterface on picture, I cant see booting menu on webinterface

HDMI output is out, so I connect AV jack, which I found and now Ive got some picture. I am going to use it as an wifi int radio player. Should be nice to have possibility to change boot slot from web interface in define image, anyway. Thank you for your time