Hey there, welcome and great that you got an awesome red K-50!
But I think you might be equating some different concepts here. For example, the lens being soft is not the same as AF problems. To test its "sharpness" (quality), you need to use a tripod, 2 sec timer, set lens to 35mm, camera to Av mode at f8, ISO 100, and manually focus on an object at a reasonable distance (maybe using live view). This should be done in bright, natural light. This is how to test if the lens is "sharp"
AF is another issue. In live view, you can use CD AF (contrast detect), which is precise, but slow. just make sure its not focusing on something with more contrast, for example a contrasty background behind the object.
Outside live view, the camera uses PD AF (phase detect). The AF adjustment only applies to this one, as it may misfocus, but it is fast and works even in dark conditions. The problem people often have is that they don't know which AF point is being used. And the other problem is that the AF areas are actually much bigger than the little AF overlay in the viewfinder (the little red light that lights up). so maybe the camera is locking focus, just not on the object you want it to. Anyway,
this is a good link to start with. This is common accross all brands, which is why DSLRs have AF adjust function and test charts and such.
The other thing to keep in mind are shutter speed and ISO. A high ISO can cause so much noise, the photo looks unsharp. The other problem might be slow shutter - as then the handshake will be noticeable and the photo will be blurry. This is why for tests you need to use lowest ISO and a sturdy tripod.
It would be great if you could post some photos so we can help you diagnose the problem. And keep the exif info in the photo, so we can see aperture and everything.