Download and Install CyanogenMod 10 Preview ( Android 4.1.1 Jelly Bean) For Galaxy S3 GT i9300

Android 4.1 Jelly Bean keeps the basic look and feel established in Android 4.0 but  includes a number of new features including a speedier user interface, an improved notification section with support for rich media, and the new Google Now voice search utility which is Google’s answer to Apple’s Siri.
What is different CM 9 and CM10?

The Android 4.1 Jelly Bean version of CyanogenMod be modeled CM10. Clock here for the video to know more about CyanogenMod ROM.

Now, the developer’s team at CyanogenMod released a preview build of the custom ROM for the Samsung Galaxy S3 on Tuesday. CyanogenMod is an open source replacement firmware distribution based on the Android mobile operating system for smart phones and tablet computers. It offers features and options not found in the official firmware distributed by vendors of these devices.
According to the XDA develpers member, XpLoDWilD that this Custom ROM, CM10 for Galaxy S3 GT i9300 still in the testing stage and the known issues includes:
- FMradio, heh!
- Camera is unstable, though taking pics should work
- Wi-Fi tethering is semi-broken
- Transparency issues on homescreen #blamesamsung
- Some audio issues #blamecodewo
Here is tutorial on How to Install CyanogenMod 10 Preview On the Galaxy S3 GT i9300:
Your phones must have rooted access and Installed CWM Recovery. Here is the Tutorial how to.
Step 1:Copy and paste the downloaded “CynogenMod10 Preview (zip File)”  and “gapps-ics-20120429-signed.zip”  into Galaxy S3 external SD card storage.
Step 2:Power Off your Galaxy S3.

Step 3: Press Volume Up + Home Button + Power Button until your Phones boot into CWM Recovery Mode. ( This step is almost same to boot your S3 into Downloading Mode, refer here for more info)

Step 4: Select wipe data/factory reset, then select Yes. (Note: this step will delete your Galaxy S3 data, so you can refer hereon how to backup Galaxy S3 data).
Step 5:Press volume down until option “Install Zip From SdCard”, then press Power button to select “Install Zip From SdCard” .
Step 6:Now chose “ Choose zip from SDCard”
Step 7:Press volume down and then Power button to choose  “CynogenMod10 Preview (zip File)”
Step 8:Press volume down and then Power button to choose “Yes- CynogenMod10 Preview (zip File)”
Step 9:Now is the process install  “CynogenMod10 Preview (zip File)” .
Step 10:Now install Google Apps. Press volume down until option “Install Zip From SdCard”, then press Power button to select “Install Zip From SdCard” . Now chose “ Choose zip from SDCard”. Press volume down and then Power button to choose “gapps-ics-20120429-signed.zip”. Press volume down and then Power button to choose “Yes-install gapps-ics-20120429-signed.zip”.

Reboot your S3 after installation complete. That’s All!
source: XDA,XpLoDWilD