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)
Your keyword includes “upd,” which implies updating from an existing version. If you already have a custom ROM (e.g., Android 4.4 KitKat) and want to move to 5.1.1: gti9100 firmware 511 download upd
Download and install the official Samsung USB drivers for Windows to enable communication between your PC and phone. Samsung Galaxy S2 (GT-I9100) , official software updates
Resurrection Remix: Known for high performance, stability, and extensive customization. Perform a full backup, including a Nandroid backup
The Samsung Galaxy S II (GT-I9100) is a legendary smartphone. Launched in 2011, it shipped with Android 2.3 Gingerbread and officially ended its life on Android 4.1.2 Jelly Bean. However, for enthusiasts and budget users, the device is far from dead. Thanks to the aftermarket development community, you can now run Android 5.1.1 Lollipop on this aging hardware.
It seems you’re looking for the GT-I9100 (Samsung Galaxy S II) firmware version 5.1.1 to download and update your device.