How to turn off ad option?

It's free, I know.
Upon I found the ad option, I turned it on thinking this may reciprocate the website.
But I find some bad, terrible, sexy ads showed, so I determined to turn it off!
However, I failed to.
The option is NO, but another option right under that one is ALL!
I tried many times to turn it to NO, but I failed again and agian.
Ads remain to be seen, enve though I've turn one option off.

What should I do to solve this problem?

You can only permanently disable ads if you buy the points for that. If not you can choose to make them visible only for Guests so when members log in they won;t see the ads anymore. You can do this from admin panel=>Misc=>Points management=>Configuration and look for this option "Ads are disabled. If you wish to contribute, you can activate theme by yourself thanks to this option." and choose "Guest". To buy the option to permanently remove ads click on the "Add" button next to this option "The ads are not disabled."

I selcet "Guest" and pressed "save" button.
After I check it, it is "All" again.
I tried many times, what should I do?