Hi Lynn,
Do you want to install a new theme?
If so, you can go to your WordPress Admin Dashboard and then look for the menu on the left hand side that says:
Appearance - > Themes
You will then see a new page and at the top there is a button that says 'Add New'
If you click on that you can then either search the WordPress repository for a new theme or if you have downloaded one already click on 'Upload Theme'.
If you have written blog posts or created pages these will not be lost when you change you theme but it is a good idea to backup your site either by using a plugin or a third-party backup service.
It would be my pleasure to help if you have any more questions.
Good luck with your new theme :-)
Luke the Daft Duke