This achievement is pretty straightforward. Whenever you're given the option to mod your vehicle (center section of the home hub world), you can increase your vehicle's armour or weapon for gearbits. I'm not sure of the exact amount, but you'll need no more than 10 thousand gearbits, which you should be able to accrue naturally through the game. You'll need to fully upgrade BOTH armour and weapon for the achievement to pop.
Edit #1: Sea vehicles are significantly cheaper to fully upgrade, almost 1/4th the price of a land vehicle. If you own/bought a sea vehicle, I suggest spending your gearbits to upgrade it instead of a land vehicle. It'll save you both time and money.