Most ISPs use QoS and filter it by the MAC address on your DSL/Cable modem. An accelerator does nothing, and will not allows you to break the QoS.
You can only download as fast as the host can upload, and as fast as the QoS settings on your ISP allow you to. When you call your ISP and upgrade your connection speed, they do not physically change anything. All they do is change the settings in QoS to allow you more bandwidth.
So, there really is no way an accelerator can make your connection faster. Unless by accelerator you mean hacking your modem and your ISP.