In JS128 is J6
In other of my MMC is on/off jumper , in DIVMMC AY is dipswitch number 1

So, download Eprotector from Velesoft page, velesoft.speccy.cz/zx/divide/software/divmmc_eprotector.zip

Unpack it to card
Copy new esx dos flash file to card, ESXMMC.TAP

1. Run mmc as normal, load Eprotector, remove JUMPER, press E for unprotect rom
2. Insert jumper
3. Reset MMC
4. load ESXMMC.TAP
5. remove JUMPER
6. hit any key and wait, border start flashing, this take few minutes
7.When is done, copy new esx dos files to card, insert jumper and run Eprotector Again
8. remoe JUMPER and Select option D for protect Eprom
9. Insert jumper

DONE

If flash utility say, CANNOT FLASH, try format memory card with default options.