You said that your phone already had Clockwork installed when you got it? You obviously didn't buy it new because it doesn't come with the phone. Like Darren said you really need to educate yourself before you go messing with flashing custom ROMs and kernels. Check out the wiki here:
PPCG-Sprint Epic 4g Wiki
and then check out the wiki on xda:
Samsung Galaxy S/SPH-D700 Wiki