Hi, Can anyone tell me how can I hide (disable) fields about date and that admin wrote a post? You can see that in the uploaded image.
That decision is made by the theme you choose. If you don't have the option to change it, you can edit the php code (if you know how) or change themes. For $50 you can by a push-button theme creator called Artisteer http://www.artisteer.com/ - to create your own themes and choose whether or not to have this info displayed
As Steve said, it would depend on the theme you are using. Generally, you would have a re-usable Php function that will render that information into an Html format. The function will get called somewhere within the Loop in page.php, single.php, and/or more files in your theme directory. If the theme you are using is available on the Internet, an Url would be nice. Then we can look that information up for you. Otherwise, you will have to dig around the code of one of those files and post it here for viewing.
Don't forget looking at other files which may have that code such as page.php, archive.php, category.php, etc.