Neither. Simply using Bitcoin as a mode of payment won't affect its price. What affects its price is of course the demand and supply of it. The demand of Bitcoin comes from us when we determine what is the fair market value of Bitcoin, it is also affected by other factors which cause a stronger buyer side or a stronger seller side. Think about it this way if Fiat currency is being used daily in your country why does it not increase in price over time? Because the demand and supply still remains the same.
Definitely using bitcoin cause increase in the value of bitcoin, because when more and more bitcoin circulate in the market more and more people will touch with bitcoin and thus the demand for bitcoin will increase and so is the value. Decrease here is out of sense because I think the value of anything will increase only when I use it and if I ignore something the value for that thing will decrease.