How can I get storage onto my phone
Here is my Problem:
I deleted EVERYTHING off of my iPhone 6, yet when I check my usage it is still 10 GB. I really need to backup my whatsapp chats from this old phone, so I can keep all the my chats on my new iPhone 6s, but the thing is I cannot back up the whatsapp chats because there is no space. So my question is, how can I back up these whatsapp chats with no storage and get all my chats on my new phone, OR how I can gain some storage by removing what is taking up 10 GB.
Thank you
iPhone 6, iOS 9.2.1