[Q] How to root and install ROM topic

Hi everyone,

I just bought a galaxy S3 canadian model (reference below), I noticed that the battery in standby mode consumes a lot, they told me that you should rooter and install a rom from this website.
I want to know how to do these manipulations step by step knowing that I am a beginner

Thank you

Numéro du modèle: SGH-I747M
Version Android: 4.3
Version de la bande de base: I747MVLUEMK5
Version kernel: 3.0.31-2140838
se.infra@R0304-04 #1
Tue NOV 19 19:35:04 KST 2013
Numéro de version: JSS15J.I747MVLUEMK5