There isn't a specific time frame in which you should change or replace your nozzle, but generally you should change your nozzle every 3-6 months. This really depends on how often you are using your 3D printer, what kind of filaments you are using, and how high or low the quality of your nozzle is.

How often should you clean your 3D printer nozzle?

Poor quality or cooked/burned filament can leave residue in your nozzle. Even PLA can solidify in the nozzle over time, so we advise flushing it through at least every 200 - 400 printing hours.

Is a smaller nozzle better?

Now in theory, smaller 3D printer nozzle sizes do allow you to achieve better precision. But for a lot of printers, especially lower priced or older models – a smaller sized extruder nozzle isn't necessarily going to make a difference unless your printer supports the higher resolution necessary.