Hello,
To get 100% correct demo content installation it would better to use the clean WP. But if you already created your own products, categories then the only way is to install the new demo over the existing one (XStore > Import Demos). You may face mixed images after the new demo installation and will need to edit elements that use the wrong images(from previous version). There is no other way. Either DB reset (but you will lose your products) or installation over the existing demo.
Regards