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 is an iconic device. It really set Samsung on the map. It is a very old device with official support stopped for it ages ago. But CyanogenMod team have continued the support and have come up with CM 13 ROM for this device. Using this ROM, Galaxy S2 can be updated to Android 6.0. A detailed guide on how to install this ROM is given below.