Kernels are basically boot images that you have to flash via bootloader. As of kernels itself it is that part of the operating system that acts as a middle man in the communications between the hardware and software. Interested people can read more on it here.
You can find the kernels for each ROM inside the zip file for the ROM mainly named as boot.img. For convenience you will find links to some kernels of Resurrection ROM builds to flash.
To flash the kernel first of all boot into your bootloader (Vol Up+Power). Download the kernel you want to. It will have a .img extension. Rename the file to “boot” without the quotations. So the file now becomes boot.img
The renaming is optional and it will just help in the flashing process.
Place the renamed file in the ADB folder. You can download ADB from here if you do not have it yet (which is highly unlikely).
Connect your phone to your PC via USB in the bootloader mode. Open the CMD window inside the ADB folder ( Press Shift+Ctrl+Right Click on a white space of the folder)
Type in the following command to flash the kernel :
2. Custom kernel by X Anwar
3. Kernel from Beta6.8:
4. Kernel from Beta6.5:
5. Vital kernel for Beta6.4:
6. New kernel by quanganh2627 (v6.3): (it has call issues)
7. kernel by Tran Huu Tin (boot-fix.img):
8. + Old kernels by quanganh2627 ( for his Resurrection Remix V5.5.x. rom)