best way to clear iphone memory

What do you mean by "clean your phone memory"? If you want to return your phone to factory state, deleting everything on it, start here:

Restore your iPhone, iPad, or iPod to factory settings - Apple Support

If you mean something else, please explain.

Duplicates of what?

To remove apps, see here:

Delete apps on your iPhone, iPad, and iPod touch - Apple Support

That would be a question for WhatsApp Support.