Problems with WLED on Shelly RGBW2

Hi all!

I flashed a Shelly RGBW2 with WLED 0.14.4
It works, but now, when I power on the Shelly, I get a WIFI connection, but when I want to switch on the lights, it crashes. The lights are on, but no more WIFI connection.
Then I want to power off and on again, I want to flash 0.15.0, but Upadte failed.
I took “WLED_0.15.0_ESP8266.bin”, that should be the right one.

Anyway, I want to go back to Shelly original SW. Is that possbible? How?