Hi there, you can do a live preview of the Ari theme on your blog here: https://mrsmrsblog.wordpress.com/wp-admin/customize.php?theme=pub%2Fari
(You can preview any theme by finding it under Appearance > Themes and then clicking "Live Preview").
You can find out more information about the theme here: http://theme.wordpress.com/themes/ari/
And see the theme demo here: http://aridemo.wordpress.com
Once you change a theme, your widgets carry over. In the rare case that your widgets don't show, look for them under Appearance > Widgets, in the Inactive Widgets section at the bottom of the page and re-drag and drop them into the appropriate section.
I hope this helps - let me know if you need further assistance!