[Q] help root s3 4g i9305n

need help rooting my phone swedish tele2 s3 4g gt-i9305n
I am new 2 this so if someone can explain the benifits i gain by rooting my phone. I don´t know if this is the place 2 ask as i said im new on xda.
all tips and tricks is welcome. can i change the android system 2 win7phone or something else.
but if its a good thing 2 root i hope that someone can help me
thanks
andrew