My security is weak, how can I change it?

Pending a reply to questions already posed by other members attempting to help …

… it might be related to your WiFi setup.

If so, see this article:

Recommended settings for Wi-Fi routers and access points - Apple Support

Check your router.

The Weak Security message means your base station is configured with an outdated security mode - it doesn't meet the latest standards and may leave you at risk.

The solution is to check your router's configuration. It may also need a firmware update to support the latest security standards, known as WPA3.

Who told you this? Someone trying to sell you something?

Can you please give us more details.

*What* says this.

*What* exactly does it say.

If it is on the Mac, can you provide a screenshot?

Right, so follow the document Chattanoogan provided. I am going to guess you have a password like "123456"