How to Install Official CM 11 ROM on the Samsung galaxy S3-GT-I9300

Tools Requirements:-
1. Charging Your battery up 80%.
2. Install your Devices driver in your computer.
3. Your device must be rooted and install CWM/TWRP recovery.
Must Read:- How to Install ADB Drivers of any Android device with PdaNet.
Must Read:- How to Root & Install CWM Touch Recovery in Samsung Galaxy S3 GT-I9300
Must Read:- How to Root Any Android Device.
4. Download Official CM 11 :- Click Here to Download
5. Download Gapps.Zip File:- Click Here to Download
 Installation Process:-
1. Download CM 11 custom Rom in your Computer and paste in your External SD Card.
2. Switch Off your Devices.
3. Press and hold "Volume Up + Power + Home button" then go to "CWM recovery mode"
5. Then go to backup & restore -----> backup (wait 15 to 20 minits)
6. Select “Wipe Data/Factory Reset”, this will clear all previous ROM data and your applications.--->yes
7. Select "Wipe Cache Partition"----->Yes
8. Then Go to advanced---> Select "Wipe Dalvik Cache" ---->Yes
9. Then go to Install Zip from sdcard.---->Choose zip from sdcard.---->Select Zip file to sdcard.
10. Select Yes and the Installation will Start.
11. Again select “Install Zip from sdcard” .---->Choose zip from sdcard---> Gapps zip file this time and install.
12. Reboot phone after installation is Complete.
Enjoy

The phone will take 10-15 minutes to start and initialize all the services & apps because this is the first time you are starting a phone after installing ROM. Don’t be hesitate and wait for complete process.