Simple Ralph, In your dashboard go to appearances - themes and then search for themes ... you can use the filters to make the search easier. Once found click on install and activate. You can also buy themes too. If you do this in themes click on upload to add it.

Any problems just shout ;)

Log into your site dashboard then navigate to Appearance > Themes. Click on Add New and search for what you want. Once you find it, install it then activate it to switch to the new look.

Easyenough to do, to to appearance in WP dashboard, then in the theme section either search for the theme you want, or you can choose one of the default templates that may be in place .