Samsung Galaxy S2 (GT-I9100) , official software updates ended at Android 4.1.2 Jelly Bean. To get Android 5.1.1 (Lollipop) , you must use unofficial Custom ROMs such as CyanogenMod 12.1 or OmniROM. Matthias Kerstner Essential Preparation Backup Data : Flashing a new ROM will wipe all user data . Perform a full backup, including a Nandroid backup in recovery. Root & Recovery : Your device must be rooted and have a custom recovery like CWM (ClockworkMod) installed. : Ensure your battery is at least 80% charged to prevent power failure during the flash. : Install the latest Samsung USB Drivers on your PC. Required Downloads : Download the Android 5.1.1 ZIP (e.g., CyanogenMod 12.1 ) for model : Download the Google Apps (GApps)
Once the ROM is finished, go back to Install and select the GApps .zip file. This ensures you have the Play Store and Google services. gti9100 firmware 511 download upd
Connect the Galaxy S2 to a PC via USB and move both downloaded .zip files directly to the root directory of the phone’s internal storage or external SD card. Samsung Galaxy S2 (GT-I9100) , official software updates