I just uninstall thru the OS manager. If you go to menu > settings > applications .. find the app you want to delete, click it, and theres an option to uninstall.
As for the calender, have you even tried looking? Theres a app in the app drawer that clearly says "Calender" so I don't know how you could miss it. If you would like a calender widget, then hit "+" > Widgets > Calender