I need to change the key, i saved the wrong file

Are you referring to form encryption?

I see you have one form that is encrypted and shared with polarisalpha. 

You can contact that user and ask if they have a copy of the private key.

Note that there is no way to decrypting the form without a private key. We don't store them on our servers. So you could be really stuck if you cant find it.

Encrypted Forms and How to Use Them