I have had my JGAurora A5 printer for a couple of years, and I have printed a ton of things.  The only trouble I have ever known that I had was during the beginning of Covid and all of the filament went away, I did end up with a few spools of crap, one of which was so bad I actually threw it away.  I stick with ESUN PLA+ and Gizmodorks TPU and have been happy.  So far passive drying (waterproof ammo can and desiccants) have kept my filament in shape.  I use a 3d mask from the thread on here every day.

And then I tried to print some parts that had to fit, and it all went to hell.  I struggled with the wildfire lower and a few of the things from Defcad.  Then, has anyone ever seen an all in one 3D printer test printed with BOTH tree supports AND Fuzzy skin?  It's prettu bizzare, kinda cool, and utterly useless for its task.  And finally printed a 3D Calibration Ruler.  This illustrated what I already knew, my printer prints too big.  10cm?  Nope 10.62.  A 10mm hole? Nope 9.71mm  There isnt a single measurement on this thing that is correct.  

Unfortunately, my printer was pretty good to go out of the box, it was even level with almost no effort.  So, I have never had to mess with it much and try to troubleshoot it and that means I am kinda lost on even where to start.  Help?

Double check your extrusion rate & do an extrusion calibration to see how accurately it delivers filament.  Plenty of videos on the topic to guide you.  Tweaking the extrusion rate would require a firmware update.  

Even if the extruder is dead on, some filament/temp combos are going to require you to use a different "flow rate" to get accurate dimensions. Your combo is possibly extruding more material than is needed with the default 100% flow rate.  Depending on the slicer, it may be easier to use a flow rate % lower than 100 or, alternatively, to tell it the filament is fatter than it really is (it will extrude lesser amounts if you tell it the nominal filament diameter is 1.9 mm rather than 1.75).   You may need to do some trial & error prints to find the sweet spot for your filament & temperature. Print a small test, measure, tweak settings, print & measure again til happy.  Once you find it, make a note so any time you use that filament brand/color/temp combo you will know how to get accuracy.

More often it is because of model translation and the way the slicer interprets it.

STL while the most common and most supported 3D printing format, really is a crappy file type with the exception of being free....
Seeing as it can't do arcs when you export to STL you just get a bunch of triangles forming a polygon with a lot of sides that resembles a circle but is not an actual circle. Then when you put that in to a slicer it has to try to interpret it and you just compound the issue.
It is really impressive just how much more accurate you can make holes if you use a file format that supports arcs.

Someone recently posted this, and it is a pretty good overview of the issue.
https://hydraraptor.blogspot.com/2011/02/polyholes.html?m=1

All you actually need is the ability to send GCODEs to change the extrusion rate. "M92 Exxx" will change the extruder steps.  Can put this in a GCODE file, send over the terminal/USB connection....  Firmware update is not required.