Go to Settings > Global Settings in the admin UI. Click the "Add configuration setting" button to create a new setting. The name of the setting is "ui.admin.menu.disable" (without the quotes). The value should be a comma separated list of the menu items you want removed such as "Articles, Posts, Books, Events" (without the quotes).
You will have to refresh the admin UI in your browser window to see the changes. If that doesn't work log out then log back in.