Need help bought wrongly rooted S4

[hre2stay]

The original carrier is three but the phone is unlocked. I know very little of rooting. I only discovered it's rooted as I cannot upgrade the firmware it is enforcing android 4.4.2. I have used root checker and it says Root access Is not properly installed so someone has botched the job clearly. Can anyone advise me what to do and what you need to know to help me restore it back to factory settings. I'd upload the about phone in settings screenshot but unsure of how to do it. Any help is appreciated. It's an GT-I9505

 

[anon(9424572)]

I have a 3 branded S4 unlocked to any network & there's no update available - checking via phone & kies - as mine still shows 4.4.2. I am in the UK.