It is possible to upgrade, but I wouldn't bother. It's false economy on a bike with such a low price point from new. (I'm not dissing your bike) I would ride your Apollo as much as you can, get a real taste for the sport and if it grabs you add to your upgrade fund and buy a better bike. You don't need to spend loads to get a good all rounder that will see you sound for years, or until you skill level demands more.
To hit their price points department store bikes have to cut every conceivable corner. Frames made of metals that are prone to warping/corrosion. Sloppy welds. Nothing is heat treated. Rims that are barely round, tortured into shape without regard to even tension and without any spoke prep. Bearings are not sealed, and made of low grade steel that is prone to flaking. Fork bushings made out of the same plastic as your cutting board that wears almost immediately. The list just keeps going. Hanging a couple shiny parts on it is just not sufficient to turn the bike around.
If money is a concern, find a friend that knows a bit about bikes and buy used entry level bike from a person who has cared for the bike.
Despite what has been said above "Frames made of metals that are prone to warping/corrosion. Sloppy welds." The frame looks like a solid chassis to build upon if you are on a limited budget and I've got to admit it looks pretty good in spite of the criticism heaped upon it.