How can I remove all my smartsheet contacts?

Dear Sir,

Few month ago, I was distributed custom contact list to my users for bulk upload.

By the way, We had change of several team name.

So I tried to bulk upload again. but It was not changed.

Thus, I want to remove all contact list on my smartsheet contacts.

How can I do that easily? I cannot found 'Clear All' button in system.

I am waiting for your kind helps.

Best Regard.

Kisoo.