Things required before you start the update
One ds console, you need to use a DS console to do the update,
SD card which will be stored the firmware and update files.
Buy ace3ds flashcard: http://www.dsflashcart.com/
Step1: Download the latest Ace3ds firmware V1.21 from the official site. After you finish downloading, just unzip it and put all the files in the root of your sd card.
Step2: Download the last Ace3ds update patch from the official site. Just as the same methiod, extract and put all the files in the root of your sd card.
Step3: Put the sd card in your ace3ds card, then put the ace3ds into a DS console. Power on the DS console.
Step4: Just access the ace3ds menu, and click the "game" folder, then you will see a file named "3DS V4.0.0-7", click it and start the update process.
Step5: It will take about 5 mins to finish the updating, do not power off during the updating.
After the ace3ds updates successfully, the icon will change to "Deep Labyrinth".