wifi network through a long range pc antenna legally on their account

i have a home pc that has a usb antenna that picks up signal across street and i am on their account. i was issued a password from them that is not strong. avast wants me to change my password to something stronger but i cant because i will no longer be on his free internet that i am receiveing.i dont believe they have antivirus because he is a geek that says im better off without an antivirus much less a vpn. so what should i do? avast is constantly telling me to change the password but i could be disconnected from service …wth

Either get your neighbor to change to a strong password or, disregard the Avast warning.