Go to Dashboard > Appearance > Themes
browse themes until your find one you like and click “activate”
or type in the name of the theme you want to use and
click the “activate” link when it appears
After you change your theme all you need to do is go here Dashboard > Appearance > Widgets > Inactive Widgets and re-install them where you want them to appear. The widget contents and settings will be the same as they were prior to changing themes.