Planning to restore iPhone 4S

[michali]

As my phone is giving some problems I am considering restoring it before returning it to the store, to see if I can fix it! Before I do, I want to make sure I know what I am doing! I have saved all my camera roll to my computer but not sure how I would get them back onto iPhone once it is restored. I have backed up the the phone to both the computer and iCloud. However, if I restore I would prefer to set it up as a new phone so would not use the back up. Would iCloud automatically replace all my contacts? I presume a restore would not affect my SIM card? Any advice please before I do this restore?