WordPress has Twenty Twelve installed by default. You can change it by going in the Appearance tab on the left in Dashboard.
As you move your mouse over to the Appearance tab, a new menu will pop up, displaying a variety of options, including the first option “Themes”. Click on Themes, and then it will open the “Manage Themes” tab. There is a tab on its side namely “Install Themes”, click it. It will give you option to search. You can search theme by color combination, columns (number of columns), width (Fixed or flexible) and even search by features and subject of your blog.
Not only that you can also upload your own created themes or the downloaded premium themes. You can view featured themes (that are currently trending on WordPress) and also see the newest themes on the block by clicking on newest tab. The Recently Updated tab shows the themes that have been updated recently. A nice way to look at the themes which are getting updates regularly.
After you search a theme you are given three options. You can install it right away or you can preview it before installing and you can also view details of the theme.
Each theme you install gives you different options. Some give you header customization and menu option while some don’t support them. If header is changeable the header option along with theme options will appear in the sub-menu of Appearance tab.
You have to play with the theme options which vary with each theme so we cannot provide details for them for now as there are over thousands of themes. However feel free to send us your queries in mail and we will reply you as soon as possible.