First I'd like to say I am not responsible if anything goes wrong with your 3DS. You will be doing this at your own risk. AND DO NOT UNINSTALL ANYTHING EXCEPT FOR THE APPS YOU SEE ON YOUR HOME SCREEN. Like the sound app, miiverse, mii maker, (don't uninstall if you use miis) and the camera app. Also DO NOT uninstall the Settings app it counts as essential. (Don't uninstall any of the mini applets like the friends app or the browser as there is no point.)
You will need...
How to delete system apps that are useless to you on 3DS (CFW needed)
You will need...
How to delete system apps that are useless to you on 3DS (CFW needed)