I am in the middle of switching my ISP provider and unfortunately there is more to it than being fed up with one, and expecting a smooth move to another.
To compare ISP's :click here
to get essential facts before you switch :click here
One more thing,; if you do switch in the end, you need to find out whether you have been on something called "LLU (local loop unbundling) service". This is a process whereby ISP's use their own equipment/tags in local telephone exchanges, thus you are receiving greater speeds (in theory).
However, should you deceide to switch your ISP, this LLU tag need to be removed (lengthy process called "cease and re provide") and might cost you up to £ 60.-- and leaves you without broadband for weeks!!