You would have to download a KMD wallet and then import your private key. The wallet would then have to sync with the network and then your balance would show up. Once you've  synced to the latest blocks, you goto login into your Bittrex account, find the KMD wallet click on the + deposit address and copy it.  Put that it into to send address of your wallet. Double check you got the whole address look at the begging letters and ending letters to ensure its correct. Then put in a very small amount to test send to Bittrex to make sure everything is good to go. Maybe even send it back to the wallet as a test as well...