Hello,
Have checked all the server requirements before the installation https://xstore.helpscoutdocs.com/article/60-xstore-theme-requirements ? Go to the Dashboard of XStore to see your current values, for example – http://prntscr.com/sp6lb6 Your hosting provider should be able to help you increase the required values.
Let us know if you need any further assistance from our side and which exactly demo version do you want to install.
Regards