Quick help: Go to Pages -> Sharing.
If you want to decide what photo and what text to show when someone shares the link to your event site on Twitter/Facebook/Linked in you can do so by clicking on “Pages” in the menu and then “Sharing”
You might have to "debug" the link after hitting save on our site to make sure what you edited show up correctly. You can do this here: https://developers.facebook.com/tools/debug/sharing/
With pages such as LinkedIn the information is cached which means they save the core information about the site. You can add, for example
to the end of the of the URL to make LinkedIn view it as a completely new site.