Update doesn't start

I tried to update my head unit according to info on Joying blog, during update there was some error saying that theres not enough space and the unit restarted, since then no matter how I try theres no update pop up after connecting usb flash drive. Is there a way to update my unit manually? Why was there an error with storage space? To update I used 4 GB flash drive, additionaly there was a 1 GB micro sd card connected (maybe that was why there was no space?)

Please help,
Kind regards

Edit: mines android 6 and I would like to update to android 8