There are several online sites which are providing free flash files, however you will need to download updated firmware always. If you will flash your phone with corrupted firmware, your phone will go to dead.
Remember: Please one thing keep in your mind that, you will need to must take a backup of your data before flashing, otherwise you will lose it and phone will be restore in its original settings. You can safely recover your backup data to phone after flashing.
Now follow provided links below to get the latest firmware of your phone. If you are facing trouble or download links are not working, please contact us via commenting. We will help you very soon or kept changing in download links.