The Samsung Galaxy S II (GT-I9100) officially only supports up to Android 4.1.2 (Jelly Bean). To run Android 5.1.1 (Lollipop), you must use a third-party custom ROM, as there is no official 5.1.1 firmware from Samsung for this model. Installation Overview
Since this is unofficial, you cannot use Samsung's Kies or standard OTA updates. Matthias Kerstner
The Custom ROM zip file (e.g., CM 12.1 or Resurrection Remix). gti9100 firmware 511 download upd
: Because custom ROMs are "de-Googled," you need a GApps package (ARM, Android 5.1, Pico or Nano version) to get the Play Store back. Step-by-Step Installation Guide Transfer Files
Overview: The most popular base for Android 5.1.1 builds on this legacy hardware. The Samsung Galaxy S II (GT-I9100) officially only
SamMobile is the gold standard for Samsung firmware. They host a complete archive of every region-specific release.
Updating a phone via custom recovery involves risks. Ensure you have the following ready: Root the phone using a custom kernel (like
CyanogenMod 12.1: A widely used option based on Android 5.1.1 Lollipop.