Is my galaxy s3 Rooted??

I recently bought a galaxy s3 from a shop that sells new and second hand phones. they told me the one i was buying had only previously been used for a few days and on inspection the phone looked perfect.

Anyway I have been trying to upgrade my Gs3 using Kies and keep getting the response " your device does not support software upgrading via kies". I don't know how to solve this problem and I've tried reinstalling kies itself because i know it can be very tempermental. Now I'm thinking the phone may be rooted, how can i check this and if so can you un-root it??? pls help a noob out