RE:RE:RE:RE:FIBEYou don't have wireless DSL. Digital Subscriber Line is carried over a pair of copper wires that also carries analog voice.
What you have is a wireless access point that may or may not be integrated with your DSL modem. You are not required to use the Bell provided wireless access point. You can connect your own access point via ethernet cable to one of the switchports in the Bell provided router and place your access point in a more convenient location.
In addition to signal strength settings as pointed out in a previous reply, things like attenuation and interference come into play as well as the properties of various wifi specifications (eg 802.11g vs 802.11n vs 802.11ac) that all contribute to speed and range.
Cancelling your service because your wifi coverage sucks is like cancelling your hydro because the lamp you bought in Europe won't plug into your North American wall sockets.