There's no such thing as too much riding, but there is such a thing as wearing your brake pads out!
You should replace your brake pads once the grooves in the pads are no longer visible. If this has happened, swapping out your old pads is as easy as releasing them with a 5mm hex key (make a note of their direction and the order of the washers) and putting the new ones in their place. It's safest to do one at a time, so you can refer to the original.
This is a pair of pads (enough for a front OR rear brake). Buy two pairs for both brakes.