Here is a list with today's Android Updates. You can click on the link next to the update to download the firmware. These updates should arrive as OTA's or on Samsung Kies. It is important to update your device to the latest firmware to improve overall performance and eliminate possible bugs.If you want to manually install the update, you can do it using ODIN.
Galaxy S3 GT-I9300
- Android 4.1.2 XXEMRG - Download I9300XXEMRG_I9300XECEMR5_XEC.zip
- Android 4.1.2 UBEMH3 - Download I9300UBEMH3_I9300UWAEMH1_PCT.zip
- Android 4.1.2 ZSEMI1 - Download I9300ZSEMI1_I9300OZSEMI1_BRI.zip