1. Install the ROM Manager on your Huawei Ascend G300. Get it from Android Marketplace Location, then install the clockwork mod recovery.
2. Connect your Huawei Ascend G300 to your PC employing the USB information cable. Copy the “Huawei Ascend G300_4.2 Jelly Bean.zip” file you downloaded to the SD memory card.
3. Restart your device in the recovery mode using ROM Manager. As soon as in Recovery Mode, go to ROM Manager and select backup / restore to back-up your information.
4. From the Recovery Menu do a total data erase (including Delvik Cache). When completed, go back to Recovery Principal Menu and choose Flash ROM from SD Card. Navigate the location you copied the ”Huawei Ascend G300_4.2 Jelly Bean.zip” file and follow the directions for installing Android 4.2 Jelly Bean on your Huawei Ascend G300. As soon as the installation is over, just reboot your Huawei Ascend G300 device, and here you go, you’ve just upgraded it to the new Android 4.2 Jelly Bean. Thank you for visiting Upgrade/Update Huawei Ascend G300 to Android 4.2 Jelly Bean