Can I root a phone thats already rooted? I bought a chinese phone thats seems to be be already rooted.
How can I be sure?
When I download apps that require root they don't work.
Can I change privledges on an already rooted phone?
Or can I re-root?
You can try installing the app Root Checker to know if your device is rooted or not. And yes you can root your device again even if its rooted. But yes first its better to check if it has the rooted privileges or not. As far as running of apps is concerned sometimes some app stop responding even if one has the rooted privileges better would be to first check things out.