Given you got it online, I assume you built it? Before buying anything, I'd recommend doing some basic retuning to ensure optimal tension and that everything is still positioned well, as things will move around over time. Installing a new groupset would be worthwhile for the experience, but I think you're better off saving for a new bike. With the entry level Shimano sets you're more or less paying for the brand name, and in my experience it's unlikely to make a big difference. You'll still have a cheap frame, likely with less than ideal geometry and materials used for its construction. That could bottleneck its performance regardless of your groupset, and the sets used on the more recent cheap bikes I've had weren't all that bad anyway. Provided you're able to get into most of your gears, prevent your chain rubbing on the derailleurs and don't have weird noise indicating energy being wasted or other specific performance concerns, it's probably fine as is. It might help tide you over if you're struggling with your current setup though.