Middle aged guy with basic Japanese economy car, I don’t need subwoofers or anything, I just want my music to be louder and sound better in general. Do I need new stereo or can I just get better speakers?
I really don’t want my dashboard torn up, I’m hoping to just get speakers. What brand and size should I look for? I am ok with having speakers up against my back window, or just replacing. Is replacing speakers something I moderately handy man (me) can do by myself??
Thanks for the advice.
Sound better? Most likely. Be louder? Probably not.
Your current basic economy car sound system has a weak amplifier driving mediocre speakers. You can certainly improve the speakers. Replacing the ones in the doors is pretty ordinary (I, a past-middle age guy, have done it on a few cars). Replacing the rear speakers won’t be too bad, if you can find the access to them. If you have any in the dash, it will be a royal pain that will have you cursing yourself.
As for volume, well, more efficient speakers may sound a little louder, but you can’t pull out more power than what is available.
My best suggestion is to replace two speakers (one left, one right) that are easiest to do, and see if that gives you a noticeable result. At that point, you can better decide the effort/payoff ratio.
Before you start tearing up your car, get your hearing checked. 
No, unless you add an external amplifier, you’re not going to be able to make it much louder. Aftermarket and OE radios use more or less the same hardware; despite some of the fanciful claims on power ratings you’ll see in Crutchfield the power ICs used in radios are all only capable of about 16 watts continuous per channel into a 4 ohm load.
And if you do decide to get a better head-unit, you (most likely) won’t have to mess up your dash at all. The DIN chassis is standard and should swap right in.
that depends how old OP’s car is. hardly anything uses a DIN size chassis anymore. if you’re lucky you at least have a “brick” radio with a faceplate. most common now, though are “integrated center stacks” where the display, control panel(s,) and radio are all separate modules.
All of the above is on the right track. Most OEM head ends are better than their speakers, especially after a few years of wear and tear. Replace all the speakers with the best quality ones of the same size you think are worth the money - start at around $35 for smaller speakers and maybe $50 for larger ones. You can probably replace them yourself, especially if you’re comfortable drilling a few holes, cutting plastic shields inside the doors, enlarging cutouts a little, etc. You should be able to get drop-in replacements for all the speakers, with the biggest difference being larger magnets that may not clear a body or weather shield edge.
That might be enough. It has been in a couple of cars for me. But then at least you’re all set to put in a $100-150 head-end with Bluetooth, a USB port or at least an AUX input, and you can’t really do this the other way around.
You’re going to need both speakers and a better head unit. Better speakers can’t really make a cheap stereo sound louder or better anymore than putting on big wide racing slick tires will make a car any faster. But the speakers have the final say, a more powerful head unit can’t make cheap speakers louder or much better, they’ll just sound distorted at volume.
there are no “more powerful” head units. Everyone, both OE and aftermarket, uses a 4-channel BTL amplifier chip which is capable of ~16 watts (clean) continuous x 4 with a 14.4 volt battery supply. That’s it. that’s all you can get. An example of these amplifiers is the popular ST TDA7388. You’ll find similar parts from companies like NXP and Toshiba. they cost about $5 each in quantity, and all have the same capability.
aftermarket head units which claim “50W x 4!!” are using nonsense “peak” power ratings.
years ago, Alpine tried increasing the power output of their head units by boosting the DC voltage to the amp IC internally to 18 volts. They dropped it a year later because they were getting too hot.
If the OP has the bottom trim version of the car and the fancier version had an upgraded stereo, then he might be able to swap them out. You can also find an owners’ forum for your make/model and I can almost guarantee that there will be discussions on there about stereo upgrades.
Crutchfield has historically been one of the top resources at identifying what will fit into a given car - the fitment options will range from “exact fit replacement” to notes like “These tweeters physically fit into your vehicle’s existing tweeter locations. In some cases, you may need to use backstraps, hot glue, or silicone to secure them. Use the factory speaker grilles.”
True. OTOH, their prices are pretty high. “Showroom” on your own conscience. 