To make your bike faster:
First of all, get the handlebar lowered by getting a flatbar and by simply fitting a race-style stem, but be carefull which you choose though, as too low may not suit you either.
Secondly, get thinner tyres with more pressure like for instance 28's, but this will also make your ride less smooth.
Finally, if you feel your gears are too low for higher speeds, get a new cassette. The 28-38-48 crank you have should be fine, but the 14-34 is a bit low. Ask yourself the question: "did I ever use the 28-34 gear yet? (your lowest gear)". If you didn't you can choose to equip something like a 11-28 cassette and you will have considerably higher gearing options and even more in-between-gears