Q: cannot delete icloud account because cannot turn off Find My iPhone

You will have to remember or retrieve the password, you can not turn it off unless you do.

If you forgot your Apple ID password - Apple Support

Thx Rysz

If you are not the ORIGINAL owner, then this is your only option:

Turn off Find My iPhone Activation Lock - Apple Support

If you are the ORIGINAL owner and you still have your ORIGINAL proof of purchase then take it to an Apple Store or contact Apple Support:

https://support.apple.com/en-us/HT201232

Apple ID - How to find your Apple ID

Apple ID - Find

Enter your old Apple ID and click Forgot Password,

Apple ID - Manage

Apple ID email address or password - What to do after you change

There is a contact link.

Apple ID Support

Apple ID Support (2)

You need to use your current password to log out. Even though it is the previous address, it wants the current password.

Cheers,

GB