First make at least 3 encrypted backups of your wallet.dat file and move atleast some of them to other computers or upload a copy to the web for storage. (make sure your password is strong) and change the file name or hide it in an image.
Then delete (or just cut/paste to your desktop) your wallet.dat file and make a new one. Make encrypted copes and Back it up just like the old one... then (make sure you don't get them mixed up!)
Copy the receiving address of your new wallet.dat. Then replace your new wallet.dat file for your old one.
Send your Bitcoins from the old wallet.dat to the new wallet.dat receiving  address.

Your old wallet should now be empty of Bitcoin but will have valid keys for Bitcoin cash.
Your new wallet.dat file will hold all your Bitcoins if you did it right.

uninstall the Bitcoin client and install Bitcoin cash client (using your old wallet.dat file) Now you can send your Bitcoin cash without fear of losing Bitcoin.

After you are done delete the Bitcoin CAsh client and run 9 million virus scans (BECAUSE FUCK THAT GOD DAM SCAM COIN!) then reinstall bitcoin client with your new wallet.dat file.


(use this at your own risk)

Bitcoin Cash is full retard it will take you 2 days just to send your BCC to an exchange to dump by the time it gets 20 confirmations it will be worthless.