Upgrade version Of Custom Recovery

I have CWM already installed on my Android device. To upgrade my CWM version, do I simply boot into fastboot and cd the new .iso over to my device? Is it realy that simple?

EDIT -- The new file that I have is an .iso not a .zip so when I boot into CWM it doesn't see the .iso.

2nd Edit --- I used this command when booted into fastboot to flash my recovery

fastboot flash recovery recovery-clockwork-5.0.2.0-olympus.img