One way to update the operating system of your Android device is using the manufacturer's technical support site. Visit the site using your Android device's browser, check whether there are available system updates for your specific model, and follow the instructions for the installation process. If your device allows interfacing with computers, you can connect it to a computer and update the operating system. However, you should consult the manual for instructions.
Another way of checking for system updates is from the device's built-in Settings application. Scroll down to About Phone if your device is a phone or About Tablet if your device is a tablet. If your Settings menu is tabbed, locate these options under the General section. In the menu that appears, tap Software Update, and then wait for your device to search for an available update. If the device finds an update and asks for confirmation to install, accept, and then wait for the update to install and for the device to reboot afterwards.
As a precaution, backup the files in your device before attempting to update it. Also, ensure the device has sufficient charge to last through the update process. Because the update file is large, connect to a Wi-Fi network if there is one available.