Improving my network - Time Warner Internet

My internet wifi signal is weak and i dont know what i can do to imrove it. i live in a two story house and the connection from the tg1672 comes one day and goes the next even when i am next to the modem theres drops. we have had techs come out and called in for support but this problem always comes back. maybe its our our tech gear or maybe its because we are the only time warner cable customers in this area when everyone else has verizon including the previous owner of this house. cant say for sur. right now i am not getting any significant pings with my connection and i am using the wifi analyzer app to adjust things. we have the time warner EXTREME INTERNET HOME WIF ULTIMATE 200. All i want to know is do i switch out the modem for my own modem and router, buy a powerline/wifi extender. i dont know what to do cause the connectio drops and i keep checking my own stuff thinking maybe its me. what can i do to improve my connection? cant go wired completely because i cant drill holles in the house.