The easiest thing would be to use a Miche one. These don't screw on like regular sprockets but instead fit onto an adapter which is in turn screwed onto your hub. You'll have an adapter on there already with the 16T. To change sprockets with this system you just need a lockring tool to remove the lockring holding the cog on.
You can also use regular screw on sprockets but you'll need to remove the Miche adapter first before you can use them. To change these types of sprockets you'll need a lockring tool and also a chainwhip to unscrew/tighten the sprocket. You'll need these same tools to remove the Miche adapter.
If buying regular screw on sprockets I'd recommend the Dura Ace ones as they're high quality, easily available and cheap (in the UK at least).