It depends on what changes you have made. If you changed any files from the parent theme “Xstore” so obviously you will loose all the changes after update since you will replace all theme files. To prevent this situation you should use child theme and do all your changes there. If you made some changes in the Dashboard (adding pages, products, theme options etc.) you won’t loose anything after update.
Also, note that after activating the other theme in WordPress (switching to child theme for example) your widgets configuration may be lost. So after doing this you will need to go to Appearance -> Widgets add widgets to your widgets areas.
