okay . first up stop panicking and all will be cool . i assume you can enter recovery mode ? switch your device off , remove the sd card and place a newer version of cwm recovery by a sd card reader ( http://downloadandroidrom.com/file/G...ible-i9100.zip
) . Also Place the rom ( the one you wish [since you want it be kitkat , i recommend you to flash cyanaosp ] ) after you are done copying both files on sd using a card reader , place the sd back and plug the battery in . boot into recovery mode and flash the cwm-kitkatcompatible recovery . after you have flashed it , reboot recovery ( under advanced ) and you'll be running cwm recovery v18.104.22.168 . Then wipe data , cache , dalvik cache ( under advanced ) and then flash the rom . reboot system and you'll be running cyanaosp .
here are a few important links : CyanAOSP : http://forum.xda-developers.com/show....php?t=2576407
P.S. : Report and feel free to ask anything and hope i helped ... do as i said and you'll be fine . All the best