the network key password is on the bottom of my netgear modem/router

where i was living, renting the landlord broke into my home with their keys unbeknownst to me and networked their computer thru my modem/router using the wireless. I have since moved but they have the network key (password) and they know where I moved and are cyberstalking me.

is there a way to change the network key(password)  I'm getting a security system installed and I'm afraid they are gonna try to hack it to break into my home. Can this be changed so they can't hack into it?