Need help with old keystore files and working with MSW contract

I made a contract back in 2017 tied to two addresses, then lost the keystore files for a while. I found them again and would like to pull some Ether out of this MSW contract, but have no idea what software to use in order to do this.

What is the current way people are restoring keystores and how do I use those keys to pull Ether? It looks like I can click "Write Contract" on the address on etherscan.io and it gives me some functions like execute/kill, but how does it know which keys to use?