With A9LH it's the easiest thing ever. Just simply download Luma3DS, open it's zip file, extract the arm9loaderhax.bin file to the root of your SD card, replace the one that might be on there. Then rename the aurei folder to luma.
Remember, arm9loaderhax.bin is similar to a boot.3dsx file. Except these are payloads and .3dsx files are not.