If you want to change your video information on YouTube, you need to go to your account page by clicking "Account" link on the homepage of the YouTube.
Then click "Uploaded Video" link under the "My Video" section.
Now choose the video you want to edit and click "Edit" button under it.
Then you can see the right panel of video information. You can change the title, description, tags etc.
Choose any thumbnail to your video, choose sharing option and other options like Comments, Comment voting etc.
And finally click "Save Changes" to save your new settings.