How to go back to Factory OS ?

So I've updated twice, once to 1720 and then to 2354, after having the same problem on both versions (stuck on text messages).

anyhow - does Restoring to Factory settings go back to the first OS that came with my Z10 device ?

and if not, how do I go back to it ?

also - is it going to remove my contacts from the sim ?

Thanks!

edit : thats the post where I stated the problem with frozen on text msg screen - http://forums.crackberry.com/blackbe...1/#post8622559