Almost positive I used Mist wallet over a year ago to generate these addresses.
I'm assuming you have the private keys then or backup files, correct? Or are at least still have Mist on the computers used to generate the addresses. If you have the keys or backup files, it's easy to import them into Mist or MyEtherWallet, or pretty much any Ethereum wallet software (I prefer those two, though there are other apps and sites) and send to an exchange address and convert to Bitcoin or fiat currency to cash out.
If you don't have an exchange account yet, I suggest making one now and play around with it, maybe using a small amount of ether if you can.
Some sites (e.g. Coinbase) will make you go through a lot of verification hoops if you intend to withdraw to USD or other "real" currency, and you can save yourself some time by testing it now rather than waiting until it's time to sell.
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