If you download the latest rev (1.5) you also have to delete your old rev 1.4 blockchain, before you start the new rev - it will re-load the most up to date version. Keep your wallet.dat file - this is where your addresses (public keys and coins) are kept. This is the same for any coins. If you are on Windows, the blockchain is located in an hidden file on your computer: \Users\(username)\AppData\Roaming\BTCtalkcoin (You have to set your File Explorer to show hidden files, to access it.)
The blockchain consist of all the files in that directory, EXCEPT the wallet.dat file that holds your keys (coins) - "my precious". The peer.dat file should also be deleted, in the case of BCC, as it pertains to old Rev 1.4 nodes, that were mingled with the PartyCoin users (unless you liked their latest party ). But not too many PartyCoin users liked BCC, as they used to "Crash" their party... you see, BCC Rev 1.4 and PartyCoin used to share the same network... BCC Rev 1.5 solved that issue.
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