What can be deleted (unnecessary items) in 1.9.4 in order to decrease the size of the hosting account?

Question

Magento 1.9.4

It seems like only a few weeks ago our Magento 1.9.4 account's full cPanel backup was around 13 GB. When I did a cPanel full Backup today - it came to around 26 GB! That seems like a lot for a store with about 3000 customers, 1600 products and and less than 5000 orders. There is no Email in our Email accounts.

The reason I would like to decrease the size is our hosting company will migrate us from Cent OS6 to a Cent OS7 machine and we are trying to make it as easy as possible for them. Are there any areas within Magento that can be deleted to make our account smaller? I have already deleted the Cache folder from within the var directory. Are there Error logs etc. that can also be deleted?