Well, for starters, it doesn't sound like you have a lot of cash to do so. And lighter parts cost money. So, I say step one would be to follow Rule #5, and HTFU. Not trying to be a dick or come off as an *******, but thats the best way to go about it.

I started out with a bike that weighed around 30 lbs (~13 kg), and that is how you should really learn. Don't start upgrading until you know what it is that you want out of your bike, and have the money to afford quality parts.