shallow well pumps and tank
In general, the installed tank is almost always the bare minimum size, and if replacing a larger one is often a better choice.

A simple test of the system is to run water from a place where you can observe or hear the pump (typically there is a drain connection there, which you can either run into a bucket or attach a hose to.) Starting with the pump not running (not "turned off", just on its automated control, but not running when you start) run water just until the pump starts; turn off the water and start timing. When the pump stops, check the time. If it's less than a minute, there is something that should be addressed. If it's more than a minute (and nothing else in the house is using water) it's probably fine.

If you run water into the tub or something, and there is the usual pressure gauge on the system, you should see the pressure fall to a certain point, like 30 PSI, then the pump kicks on and the pressure rises to something like 50 PSI and the pump cuts off, and the pressure falls again (drawing water from the tank) until it gets to 30 again and turns the pump on. Those pressures might be 20 &amp; 40 or 40 &amp; 60, covering the 3 most common settings.

If that cycle is very fast, it's a sign of a waterlogged tank or failed bladder. Bladder tanks have been the common default for more than 20 years, so it's very likely that you have a bladder tank unless someone with a major case of nostalgia for things that work poorly put the current tank in 20 years ago.

An additional diagnostic is, after the timing test; with the pump shut off and the system at peak pressure, and nothing else in the house using water: draw water into a bucket just until the pump turns on again. Measure the volume of that water. This is the "drawdown" of your tank, and there are tables which would tell you what it should be, when you have identified your tank and noted the pressures your system works between. If the amount of water you get is significantly less than those tables indicate (it will generally never be more) there is a problem with the tank.