The frequency with which you should replace a modem can vary depending on various factors, such as the quality of the modem, technological advancements, and personal needs. Generally, a modem can last several years before it might need replacing. Here are some considerations:

1. Technological advancements: Technologies and standards for internet connections can evolve and improve. For example, if you have an older modem that is not compatible with the latest technologies, such as faster internet speeds or more advanced security protocols, it may be necessary to upgrade to a new modem.

2. Changes in internet needs: If your internet needs change over time, a new modem may be needed to meet those needs. For example, if you initially had a lower internet speed but now require more bandwidth for streaming, gaming, or remote work, a new modem with higher speeds may be required.

3. Reliability and performance: Over time, modems can show wear and become less reliable. If you notice that you are regularly experiencing issues with your internet connection, such as outages or slow speeds, it might be time to replace your modem.

It is advisable to regularly keep in touch with your internet provider and inquire about any modem upgrades or recommendations. They can guide you in determining the optimal lifespan of your modem and when it might be time to upgrade based on your specific situation.