In the Theme store you will find a variety of themes you can activate yourself, enabling you to immediately modify your online store's overall design. The Theme Store offers free themes and themes for which you pay a monthly subscription fee.
Paid themes are mostly developed by third parties. They have been extensively tested for conversion tendencies, designed by conversion experts and are furthermore maintained technically and updated monthly.
If you are not satisfied with your theme, you can replace it with another whenever so desired.