If you have hacked your 3DS in the past, or you purchased your 3DS second-hand, it is possible that your console already has custom firmware. You should [check for CFW](checking-for-cfw) before proceeding.
Before starting, you may want to check your SD card for errors using [H2testw (Windows)](h2testw-(windows)), [F3 (Linux)](f3-(linux)), or [F3XSwift (Mac)](f3xswift-(mac))!
A number of methods that work on all versions are available, but require additional hardware. If possible, you should follow one of the software methods listed above instead.