One of the first upgrades that “conventional” wisdom suggests that every camera-buying photographer make is replacing the kit lens that comes bundled with a new camera. As a cheapskate photographer, you don’t want to waste money. So, is this good advice or a clever sales pitch?
Competition being what it is, none of the major camera manufacturers can afford to pass off a bad lens with even their entry-level DSLR or mirrorless camera models. Modern kit lenses are quite good nowadays and can do a very effective job within their limitations. You will see the faults of kit lenses more in cheaper construction, not in image quality or sharpness.
The flaws of kit lenses usually lie in chromatic aberration and geometric distortion. If you shoot jpeg images those flaws are usually corrected in camera. If you shoot raw images you can access Lens Profile settings in all of the major raw file editors such as Adobe Lightroom or Capture 1 Pro and others that automatically correct the visual flaws of all current kit lenses on the market today. Those flaws, once corrected, eliminate the visual image differences that most commonly distinguish “pro” lenses from cheaper consumer-oriented gear.
Of course, kit lenses usually have smaller maximum apertures than their higher-priced counterparts, so you cannot create the smooth background blur that is characteristic of lenses with f:1.8 or faster maximum apertures. That’s pretty much the only area where kit lenses differ from their more expensive counterparts. If you specialize in portraits that may matter to you. But for most photography, better photos are obtained by learning good photography technique, not by upgrading lenses. Shoot with what you have! No one will ever criticize your photos for being shot with a kit lens!