Galaxy S2 was launched in 2011. It is powered by a 1 GHz dual core processor and 1 GB RAM. It had 16/32 GB internal storage options which could be further expanded by 32 GB via microSD card. It also had a 8 MP rear camera and a 2 MP front facing camera. It originally ran on Android 2.3.4 and was later upgradable to Android 4.1.
Samsung Galaxy S2 was the device which really put Samsung on the map. It was one of the best devices launched at that time and there were record sales. But it has been long time since and the official support has stopped which means no Android updates. However CM 12.1 ROM is available for Galaxy S2 which will update this device to Android 5.1.1. Follow the guide below.