Uninstalling pretendo

Hello, i will like to uninstalling pretendo and also unmod it, because i dont use my 3ds and i want to sell it, so Can anyone help me please?

To uninstall Pretendo, just open Nimbus and select the Nintendo option. To make sure that worked, open the Friend List and make sure that your Nintendo Network friend code is displayed. Then, you can follow the Uninstall CFW - 3DS Hacks Guide (make sure to read the warnings there).