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things you need: 3DS/2DS, SD card 2gb-128gb, computer with SD slot, 30 min to 1 hour
• I used
this guide - it goes step by step and is considered the go-to guide
• in brief, you need to download a few files/softwares (MSET9 and Python), then format the SD card to access your DS's data files
• there, you'll prep your DS using a special hack in Mii Maker, change some settings in the MSET9 script, then download & install boot9strap
• some other apps will be downloaded by the script - then after deleting MSET9, Luma3DS should be active, accessing your new custom firmware :-D
• done! I would recommend r/piracy as a starting point for downloading games :-]
• besides 3DS games, you can download GBA games, use custom themes, run emulators & more! good luck and have fun!!!