Samsung Galaxy S2 — Samsung galaxy s2----network change?

I have two probs with my phone, i hope someone can help...

My sister got me a galaxy s2 for my birthday, but she had been messing around and sync'd a random email address she made up with the thingwould the (vol-up + on-button) method of restoring factory settings solve this problem for me and remove that sync'd acc?..or am i stuck with that account sync'd on my phone unless she remembers the password?

also does anyone know how to unlock to different networks with this phone?

I hope someone can help me out with this, im worried to do the vol-up + on-button thing unless im 100% sure it will remove that stupid email acc

thanx

Hi thanks fr replying,

Its currently vodafone network <<<<>>>> i want it to be o2
and i have gone to settings and ractory reset, but theres a pop up saying:

Samsung ID
theEmail@gmail.com
(and it wants password then)

its like shes gone and registered the phone to run off a single main samsung acc i think, i genuinly dont even understand how to use this phone yet but so far this email acc (and its password, which she cant remember) are linked with the phone, its kind of odd...

i have a feeling she registered it with samsung without realizing that that was actually an important thing and i should have been the one to do it..
would the hard reset remove accounts and stuff registered with the phone also?