maybe your question is "how to stop using redNAND" ?
because stopping using Mocha is easy, don't launch Mocha (either manually or from CBHC boot menu).
if you use CBHC, press home button at console boot, and select boot option : sysmenu
done.
If you use haxchi to launch Mocha, press a different button to launch sysmenu instead of mocha, or reinstall haxchi with a new config.txt to map buttons to new homebrew.
redNAND will not be used anymore.
you can format your SD card if you want to recover the used space.
If now you want to merge redNAND to realNAND (savegame, etc.), then that's another story. way more complicated. system NAND and redirected NAND are not friend and you better just forget about redNAND's content and reinstall to sysNAND.