If your NANDs are unlinked, just go into the data management section of the system settings while in emuNAND and delete the update from there. If they ARE linked, DO NOT do that (if you do, the system settings will delete everything that isn't legit on your SD card), use something like FBI or DevMenu to delete the update. Its title ID is CTR-U-EDHE (or unique ID 0x0014f100/title ID 0x0004000e0014f100), assuming you're using the US version (make sure you're deleting the patch and not the app).