[Ethereum] How to change the password to an account

Are you aware of the bug in the Mist wallet? It is exactly what you explained or did I misunderstand? If you are confident you are entering the correct pass then its likely the bug. users reported a bug, and devs confirmed that in some cases entering the correct password will fail stating wrong PW when its actually correct. You could use the Kraken json converter that would put the coins online and then send directly to your local wallet. I personally don't leave any coins other than what I am actively trading at that moment online anymore since the Cryptsy disaster. Hope this helps, search for password bug and you will see posts from people much smarter than me :) Good luck

You cannot recreate the private key file. The password is used to decrypt the key file, and then an address is generated from the private key in a non-reversible way. The private key is really the most important piece and should be backed up.