How to install KitKat on Galaxy S2 with CM 11

The Galaxy S2

Warning

The installation of custom ROMs is risky, so if you do not follow the procedure properly, you can end up with an unusable phone. Back up all your data first, charge your battery and proceed with caution. Neither AndroidPIT nor myself will be held responsible for any damage done to your phone as a result of this process.

Prerequisites

I'll assume that your Galaxy S2 (I9100) is rooted and you have already made a Nandroid backup of your system. If you're not rooted and are unsure how to root your Galaxy S2, check this S2 root tutorial. You should also backup your app data too as this process will wipe your device.

Downloads

Download the latest CM 11 Nightly for the Galaxy S2 I9100. As always, there's nothing preventing you from flashing a newer version, once it is available.
Also download the Google applications package for KitKat: gapps-kk

Install Android 4.4 on the Galaxy S2 KitKat with CM 11

Since your S2 is rooted, we will use the good old custom recovery method. As a reminder, here is the procedure:
1. Download both zip files given above on your Galaxy S2.

2. Place both files in the root directory of your S2.

3. Turn off the Galaxy S2 and restart in Recovery Mode (Home + Power + Volume Up until the logo appears or the third vibration and release).

4. Perform a factory reset by selecting and confirming the option "Wipe Data/Factory Reset" then "Wipe Cache". Some users prefer to ''Format System'' / ''Wipe Dalvik Cache'' at this point too.

5. Then select "install zip from sd card" and locate the CM 11 zip you downloaded before.

6. Click "Yes" to confirm.

7. Next, flash the gapps zip file.

8. Return to the main Recovery Menu and select "Reboot System Now".

The first reboot on CM 11 may take a few minutes. Let us know how you like it!

Via: XDA Developers Source: CyanogenMod 
Thanks to Androidpit