Resetting settings in Calibre / solving a import problem

Hi, and sorry for my bad english.
I'm newbee with Calibre (used in Windows); I've started using it to convert ebooks and only yesterday I tried to use it as a manager for my ebooks.
Since I'm not an expert I may have changed some setting I had not to; now, when I import a book in the library, in the folder it adds a number in brackets after the title of the books.
The first imported ebook has (1) after the title, the second (2), etcetera.

I would like to delete this setting, but I can't figure out how to do it.

I tried to uninstall and reinstall Calibre, but it doesn't delete the setting files, so the problem is still there.

So, I have two possible question:
- How can I solve the problem of the encreasing numbers?
otherwise:
- How can I delete the setting files after uninstalling Calibre? (I would reinstall it after that).

Thank you for your attention, Marco