CyanogenMod 10.1 nightly builds based upon the very latest Android 4.2.2 Jelly Bean can now be installed on your Galaxy S III (GT-i9300). One of Android’s biggest assets is its ability to be modified extensively, and with CyanogenMod being one of the most popular aftermarket firmware ROMs around, many people like to check the nightly builds released in between main versions.
Since these nightly builds seldom run perfectly, we advise installing on a spare Galaxy S III, as opposed to your daily driver. Following are the step by step instructions:-
Step 1 You need to root your Galaxy S III, and then flash ClockworkMod Recovery to it.
Step 2 Download the latest nightly of CM10.1 from the CM Downloads page, as well as GApps for CM10.1, which you can get by a simple search on your search engine. Once downloaded, drop them into the both into the /sdcard directory of your handset.
Step 3 You need to shut down your Galaxy S III before booting into ClockworkMod Recovery. You just need to hold Volume Up + Home + Power simultaneously to complete it.
Step 4 Take a Nandroid backup.
Step 5 You need to navigate to install zip from sdcard > choose zip from sdcard and then select your CM101.zip file. It’s best to rename the CM 10.1 zip you downloaded in Step 2 to CM101.zip so that you can locate it easily.
Step 6 Apply the same process as in step 5, but for GApps.
Step 7 From within the ClockworkMod main menu, select wipe data / factory reset, and once the process is complete, opt to reboot system now from the main menu.
Provided everything has worked properly, your device will boot into the nightly build of CyanogenMod 10.1 (based on Android 4.2.2).