Mobile manufacturers don't give software updates to each and every phone. So in this case you need to install a custom Rom (Android OS) developed by an android developer.
Follow below steps to flash a custom rom:
Before installing a custom rom, you first need to root you smartphone. Rooting grants you access to your mobile's system files. Rooting will also void your handset's warranty. So think twice before you root your device.
Once you root your device, save the custom rom file into your phone's SD card. Custom rom will be easily available online (if it is developed for your handset). Then reboot your phone in recovery mode. To reboot your handset in recovery mode download third party app which are available on Google play store. You can also access recovery mode by pressing hard keys like volume key up/down and power button.
Once you get into recovery mode, clear dalvik cache, battery stats and then install custom rom zip file. Then restart your device.
Note:- Do read installing the custom rom procedure carefully and follow it properly. Some custom roms may have bugs like wifi not working, camera not working etc. But the developer sometimes fixes those bugs and gives patches for issues.
The following site has good developers and is an authentic site for android developments and custom roms:
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