[Q] How can CWM be built in a kernel?
Well, the difference between and old version and a recent one is that the newer version has more features and maybe some bug corrections. Just like Windows 7 and 8, or iOS 6 and 7...
It's pretty hard to update your phone by yourself. You would need to learn about bootloader, firmware, rom, recovery...
And then, you should have a custom recovery. You should port Android 4.4 for your phone, and flash it through the recovery.
And maybe you would need to unlock the bootloader.
PS: What phone you have?
Sorry for my bad english.