Migrtae old Keystore files from 2017

Hey together,

I tried to migrate my old Keystore files to the "My Crypto" Wallet but it didn't work. I created them around 2017 with the official "Ethereum Wallet". I still can use this wallet to open the keystore files and make transactions with my Passphrase, but I cannot migrate them. Is there a easy way or do I have to create a new wallet adress and send my old ether to the new adress? btw. is my crypt a good wallet for storing cryptos "cold".

I want to switch because the old wallet isn't supported by the devs anymore.