Hi there and welcome
It is all dependent on your provider for the phone as the process differs (or in some cases does not exist) depending on the provider.
With which provider is the phone linked to?
ok, if it is rooted then the bootloader should not be locked.
You can confirm this by trying to flash it via Odin.
Please note, as a forwarning flashing your device can render it bricked, even if you do all the instructions correctly, if the phone is bricked then you will not be able to use it again, its the risk of flashing it, so you need to judge if it is worth it.
To flash it to the latest stable version
Download the firmware for this device at http://SamMobile.com/firmwares
Once the download is complete, extract ?(right click it and select Extract) the firmware file to a place you will remember, like a folder on your desktop.
Download Odin. Odin is a simple utility that is used to flash firmware to Samsung devices. Here is a link to one source:
Make sure your phone is off and disconnected from your computer.
Open Odin. Under Options, only "Auto Reboot" and "F. Reset Time" should be checked.
Click the "AP" (or "PDA") box and browse for the extracted firmware file.
Press and hold the following buttons in order: Volume Down + Home + Power. Keep holding them until you see a screen that says "Warning!!" at the top.
Press the Volume Up button to continue.
The next screen will show the Android logo and say "ODIN MODE" at the top left. The text is very tiny - almost unreadable. So if you can't read it, you are on the right track.
Now connect your phone to your computer via USB.
In Odin, look to the top left and wait until you see in the leftmost box "COM" followed by a colon and a number, such as "COM:4". The number doesn't matter. Once you see that, you can proceed.
In the Message box in Odin, you should see several lines of text.
Press Start in Odin.
Odin will begin processing, and on your screen you will see "Downloading" with a status bar underneath.
When Odin is successfully finished, you will see in the Message box "All threads completed".
Your phone should begin rebooting. You can disconnect from the computer.
If your phone reboots successfully into the rom, you're done and its updated.
I strongly advise you get the firmware from there as others usually contain malware built into it.
If you would like any additional information or assistance, please do not hesitate to let me know.
Else if you can take a second to rate my service by clicking one of the stars at the top of the screen then submit, that would be greatly appreciated.
I work online here but I can connect to your computer and do this instead if you wish? I have made the offer