I know my english sux sry:
Depends on the kernel but usually it is listed in the kernel thread the how to (odin or clockworkmod), clockworkmode is already on your phone if you rooted it with cf-root.
Now, to enter clockworkmod recovery, just push volume up + home + power button until the S2 bootlogo appears, then wait few seconds.
About the kernel type, i always flashed any kernel despite of my baseband, the difference is not so big.
if something is not working, you can always youse the nandroid backup (the backup done with the recovery cwm (up+home+power) and get back to the previous rom with previous kernel.
Im not really in the kernel "how to" someone else can prolly give you more detailed info, but as for me, i flashed ninphetamine 2.05 and 2.1.3 in cwm and it worked.
But.. as always, the kernel developers got a how to install in their kernel thread, so just read those and be sure about if you need odin or clockworkmod, if you are not sure, DONT flash anything until you are sure on how to proceed or wich system to use for flashing, better keep an old kernel with a working phone than have a brick to hold the papers
PS: also almost all the roms on the S2 forum are flashable with the clockworkmod, only few (like the lite'ning) are flashable with odin.
Again, i know im boring, dont proceed if you are not sure, better ask 10 times instead brick your phone
Device: Galaxy Note 2 GT-N7100 & Samsung Galaxy SII i9100 white
Rom: Rooted Stock XXAMB2(on the Note 2)
Rom2: Latest Miui (on the white S2)
Nandroid Note: None
Nandroid White S2: Stock TW Rom KF3 2.3.3