I need to change my password to stop someone using it
I am assuming you mean change the wifi password on your NOW Router ?
If so try this.
With your internet browser url address bar type in 192.168.0.1 where the router settings webpage will appear on screen.
Once the NowTV Hub Router settings page opens, select Wireless tab, then if you are asked for the username & password use admin & nowtv.
Where in the Wireless section you will see your current password in a box towards the bottom of the screen, type in your own preferred password and click on the apply button.
Make sure you keep a note somewhere safe for your new wifi password used on your NowTV Hub Router.
A factory reset of the Hub Router should default the wifi password back to it's default settings.
Have a nosy at this link, it should point you in the right direction.