Weird semi-root situation.

Hi guys,
Yesterday i have rooted a friend's phone with a laptop using the RootGenius application and all worked perfectly and the root is working good. After that, i rooted my phone wich is a Samsung Galaxy S4 Black Edition (i9505) and...well, something went wrong there. After the root, all the programs were stopping working. The installed programs were not available and i couldn't open almost any app. I did a factory reset and now it's working fine, but...the root acces it's a little bit f****d up.

If i check the root with Root Checker, it says that i have root access. The superuser app is called KingUser and i never heard of this app.
Now, here comes the problem: if i want to use a root-needed app like GameCIH, for example, i grant the root access, but i can't use the app, it says that i don't have a rooted phone...
I can use the XMODGAMES app wich is also a root-needed app, but i want to use all the root apps, 'cause why not?

I tried to install SuperSU. When i open it, it says that i need to update SU binaries. I press normal, because i don't have a custom recovery and then i grant root acces and then it says: Failed, reboot the phone and try again. I rebooted it a few times and no succes, the same thing.

So what should i do?
Should i unroot it and then re-root it?
If yes, how?

Thanks.
Have a nice day.