Bell Galaxy S3 i747m - Original Rom

[rijaesalang]

Hello there,

I am very new with Android phones and I have some questions if someone can answer me please.
I have done hard reset my Galaxy S3 couple days ago and I was trying to run "Video Hub".
"Video Hub" was giving me an error message that is "Device authorisation is failed"
Honestly, I do not mind that this app does not work but it really challenge me that the "Hard Reset" does not really clear all the information on my phone.

Here is my question.
1. Is there a way to re-format or re-install android OS on my phone? (something like returning to the beginnig of my phone when I bought it)
2. I have two ROMs (one is the Bell Jelly Bean ORIGINAL rom and Bell Jelly Bean ROOTED rom), using these ROM, can I re-install android OS without voiding warranty?
3. if my phone get "Bricked", using the Bell Jelly Bean ORIGINAL rom, can I unbrick my phone? (I saw some post that I need CWM? do I need to get additional file to download?)

Could please someone explain me? I am ready to learn new things but I need some basic knowledge. please help me...

Thanks, guys!