Resetting Wifi Password on my Mac

I think my home network security has been breached.  I'm not sure this is a HughesNet issue but more local to me.  I'm using an Airport Extreme router with a couple of Airport Express routers as range extenders.

I want to reset my network password to limit who can access my internet.  I'm hoping someone here is more knowledgeable about my iMac than I am.

I know I can access the network through my Airport Utility app.  Is that where I can change the password?

Any assistance will be greatly appreciated.  I hope I've explained what I'm. trying to accomplish.  Thank you in advance for your help.

Howard