Delete all calendars and contacts in iOS
Delete an Existing Calendar :


In iPhone Calendar, tap on the Calendars button at the top-left of the iPhone Calendar display.
Tap on the Edit button at the top-left of the Calendars display.
Tap on the calendar you wish to delete.
Scroll to reveal the Delete Calendar button at the bottom of the Edit Calendar display and tap on it.
Confirm the deletion by tapping on Delete Calendar in the confirmation display.
Tap Done at the top-left of the Edit Calendars display.
Tap Done at the top-right of the Calendars display to return to the main display.




Delete a contact : 


Select the contact's name. 
Click on the "edit" button in the upper right hand corner.  
Scroll down and select delete.


If you want to delete contacts in bulk you can use these apps :


Paid :

https://itunes.apple.com/us/app/contactdel-delete-multiple/id399148990?mt=8 
how to : http://www.youtube.com/watch?v=cHn6ABEDk1o

Free :


Download the app 'Groups' by Qbix
Link : https://itunes.apple.com/us/app/groups/id407855546?mt=8
As soon as you open the groups app it has all your contacts.
You can tap multiple contacts (a red dot to the left of each one) and
then at the top on the right there is a little white arrow that says
"actions".
Tap on that &amp; you can delete, copy, or e-mail all of the
selected contact at once.