You can add CSS needed to float the thumbnails in your site theme.
If you need to rearrange the html, in order to achieve the design, you can use external templates. I have attached News external templates. So, extract News.zip in ~/Sitefinity/ControlTemplates/News/. You will have ListPageDetails.ascx and ListPageMaster.ascx files and App_LocalResources folder. After that go to the page where you have added News control and click edit link, then switch to Advanced tab and expand Appearance group.
ItemListTemplatePath to ~/Sitefinity/ControlTemplates/News/ListPageMaster.ascx
SingleItemTemplatePath to ~/Sitefinity/ControlTemplates/News/ListPageDetails.ascx
So now you can change the html as you wish and write the needed CSS in your site theme.
the Telerik team