I have a Samsung Galaxy S3 with ICS. I want to upgrade my phone to Jelly Bean OS, but I don't have a good enough WiFi connection or enough knowledge, so I want to take the phone to a phone repair center to be upgraded. I have lot of sensitive files on it. I cant remember where some of them were in My phone. Is it possible to upgrade it to Jelly Bean while factory resetting the Phone, because the repair people should not have access to internal files ?. I can do this in my old phone by completely removing everything but I don't know about Android phones.
If you ever give your phone to a repair person or a rep at a carrier store you should assume your data can and will be looked at. Unfortunately, I saw this all the time while working for Verizon. We had reps that couldn't wait to get their hands on a phone and start looking through pictures and other private files of customers. I've actually seen reps save customers pictures to their own device! It's one of the many, many reasons I quit. Bottom line: Anything on your phone can potentially be accessed and seen.
No, it's not possible. An update by default saves all files and settings. But you should do a factory reset before giving it to the service people(be sure to backup all files before resetting).
To reset, goto
Settings > Backup & Reset > Factory Reset
After you press OK, your phone will be reset & all old files, apps, settings, etc will be deleted.