Grin Baserunner, - Flat Field-Oriented Waterproof Motor Controller for Battery Enclosures with Z910 Plug. 60V Max and 55A Peak Phase Currents (~30-35A Continuous). No On/Off switch and Unterminated. Full Product Information Page
That whole thing is a controller, I can see the MOSFETs (transistors) in there, so that's the controller for sure.
What I was expecting was that, I thought there would be a controller unit (almost always box shaped) in there, but I guess that bottom casing was working as a box.
The information was on your casing, I typed in "sc-zwk3610a" on Google hoping to at least find out the manufacture but no luck
I could not find any 4 pin Julet connector display either, looks like your electric component was specifically designed for your bike, instead of using universal parts.
The other option would be to swap the battery, display and controller (even the motor if you want). However it would be quite expensive, but you will more than likely be adding more power and range.
Your battery capacity is 187Wh, and your controller says 36V x 10A = 360W max. (and I'm guessing nominal output is 250W)
Almost any kit would surpass your current spec, but again, if you weren't looking for an upgrade, it would be an unexpected cost for you.
You can definitely do that, but there are numerous options depending on your criteria.
For example, do you want to keep it light? Because your bike will definitely get heavier if you get a high capacity battery pack (although I don't think it would be a big deal when you're riding), as a reference, the EBR spec sheet says your battery pack weighs 3 lbs, and typical ebike batteries weight at least double of that, but a lot higher capacity.
Also, how clean do you want your bike to look? Because if you get a typical controller, it won't look as pretty. Many ebike companies hide their controller inside the frame (if the frame is wide enough) but that doesn't look like an option here.
I like Grin Technologie Baserunner, because as you can see, the controller hide underneath the battery pack, which makes the clean look.
The Baserunner has 20V to 60V range, and 30A continuous and 55A max.
Your current controller has 36V, and 10A (plus or minus 1A) max. (Link Removed - No Longer Exists)
As you can see, DIY ebikes have this box controller outside, which does not look very clean.
Not to mention the poor wiring job.
As you can see, if you buy a ebike from manufacture, it does look a lot cleaner.
But you can still see the controller outside. (Although it's nicely tucked behind the seatpost, clearner wiring, and etc,)