HI, i just know a procedure on how to do it....
1st) install a plugin in spark called enigma2upgrade.
2nd) download an appropriate enigma 2 image for your receiver.
3rd) copy uimage and the other .img file to the root of an usb drive.
4th) Putt the usb on your receiver with spark iniciated
5th) open enigma2upgrade plugin and press red button to install
6th) shutt down the receiver on the back button
7th) turn on the receiver while pressing the ok button on front pannel, when you see FORC on the pannel you stop pressing ok button and click the down button (p- ) and you will se enigma2 on the pannel, then click ok button and enigma2 will start.
Best regards.