Which tutorial are you following? (send a link if you can)
GM9 is a .firm, so you chainload it from luma.
If you cannot load into it by holding start while the console is turning on, its likely the GodMode9.firm is in the wrong spot (supposed to be at sd:/luma/payloads) (that, or you don't have luma).
Also, what does it say at the bottom of the bottom screen when you hold select while the console is turning on? Depending on when it was hacked, it may have a different setup than the standard one we use today. The text on that screen should tell what firm0 exploit (B9S is the one used today, A9LH is an older one) and CFW (luma3ds, or others) was used.
Even if you are never going to use any features provided by CFW, uninstalling it is almost never the answer. You will not get banned for having it, and it does not interfere with normal operation at all. There are a bunch of risks to uninstalling CFW, including bricking the console. (can be fixed with NTRBoot and a compatible flashcart, but it costs extra to purchase one, on top of having to find where to purchase a legit one), breaking DS mode, breaking the keyboard, breaking system updates, etc.
