So I bought my phone from a friend and its rooted. When I wanted to check for a system update there isn't the option in the settings. Is this because the phone is rooted? If I unroot the phone will I have that option again?
The option should be there, even if rooted. But rule number 1 of rooted phones: Don't EVER EVER EVER perform an OTA on a rooted Android device. The update will either fail, put your phone into a bootloop, render unable to boot, or at the least remove root.
At a minimum, before attempting any update, throroughly research what changes were made to the OTA, and how to perform the update in a safe manner on a rooted device. At a minimum, you will need to hide root in order to install the OTA. But even this doesn't always work. It varies by device, and by OTA. So do your research.