To manage content types, go to Settings > Calendar Settings. Halfway down the Calendar Settings page will be the Content Types section.
To add a new content type, select the drop-down and choose any default content type. Once the content type has been selected, click Add.
Hover over any existing content type to Rearrange or Delete the content type from your calendar. Deleting a content type inside the Calendar Settings page will not remove any existing content on your calendar.