You don't need to change your resonant (bottom) heads but if they are old, worn, or damaged then it is a good idea. Also, changing from stock heads to quality aftermarket from Evans, Remo, or Aquarian will certainly increase quality of sound, though if you are newer to drums I wouldn't both right now. Hydraulic heads are very easy to tune and give a fat thumpy sound, as Evans describes them they are great for less experienced/newer drummers and/or problem drums. One thing you should be aware of though is they do not necessarily give a softer sound. They cut out a lot of overtones making the sound of your drums much more like what you are used to hearing on radio pop songs (you will hear this described as "pre-eq'ed") from your ear at the seat but they do have a very pronounced 'clicky' sound to them (you will hear this described as "stick sound") which is even worse with nylon tipped sticks. Contrary to popular belief, they do not make your drums quieter. They can reduce overtones that travel long distances and they can reduce the ability for your drums to 'cut' or project but, to a neighbor for example, your drums will be just as loud.
All in all I think hydraulics are a great starting point for new drummers. Even if you end up preferring a more open (read: ringy, resonant, etc) sound down the line these will get you started, are very durable, and will allow you to focus on playing your drums and NOT spend all your time fiddling with tuning and muffling. Slap em on, tighten them (in a star pattern) until they sound pleasing, then have some fun!