For Samsung devices, you can use tools like Samsung Kies on a computer to check for and install firmware upgrades. Manual Flashing Methods
Go to Settings > About device > Software update and select Update . If an update is available, follow the prompts to download and install it over Wi-Fi.
For older devices where OTA is no longer an option, manual flashing is often required: [GUIDE] Manually Flashing Official 4.1 Jelly Bean
To download and install Android 4.1 (Jelly Bean) firmware, you can use official Over-the-Air (OTA) updates or manual flashing methods depending on your device and current software status. Official Update Methods
You'll also need a few tools, namely ClockworkMod recovery, the fastboot files you used to unlock your bootloader. Grab them here: Android Central Forum
If your device still supports official updates, these are the safest options: