Boot into TWRP by holding Volume Up + Home + Power.
You need TWRP (Team Win Recovery Project) to flash the ROM. Use (on PC) to flash twrp-3.7.0_9-0-i9100.img.tar . samsung galaxy s2 android 13 free
Modern Android versions are much larger than Gingerbread. You will likely need to "re-pit" your device to increase the system partition size. Boot into TWRP by holding Volume Up + Home + Power
Users should expect the following non-functional or broken features: samsung galaxy s2 android 13 free
If you try the ROM and find it unusable, do not despair. Here are better Android versions for the S2, all free: