Absolutely! Your novel remains 100% your own. True Novelist may access your novel to provide statistics (daily word goals, words written, etc.) but full rights to your novel remain yours.
Your login provides the only access to your novel - your novel is not public and is not shared online.
In addition, your novel is encrypted before being stored on the server, so even if someone were to gain access to your story files they would not be able to read them.
Select a section of text and the editor will automatically popup, like this:
Click on the option you want to adjust the text.