Default Someone Please help a newbie!

ok so I purchased a note 3 recently from a friend and I am at the dreaded 27% install issue people are having for kitkat.
The phone does say custom upon starting with the open pad lock, upon checking a root checker app it seems the phone is not rooted.
I is a att phone, does this means it is unlocked? it also says under version 4.3 so i dont think its a custom rom?

My main question is, if I take this phone to bestbuy to a samsung hub will they update it for me to kitkat even with the padlock open on my startup screen?

Please keep in mind im totally new to android so any help will be appreciated! thank you!