Unable to Update System Software.

Good Evening everyone.

I've just recently purchased myself a Galaxy Grand Prime.

Whenever I tried to update my phone, it just states that the operating system on my device has been modified in an unauthorized way.

I tried rebooting my phone on safe mode and it still gave me the problem.

So, I tried connecting phone to my laptop using Kies but it wasn't able to detect my phone. It just kept on stating that my device isn't supported.

I tried downloading all the other versions of Kies as well as Smart Switch but to no avail.

Please, someone help me.

Thanks.