Best way is to match the old ones up to be sure they fit.
There are so many different pads out there...unless you know EXACTLY what you have, buying online might be a problem. It might be hard to order the right parts.
Better to take the old ones to a store and match them up so you KNOW they fit.
Watch thickness as well, be sure your disc still fits with your new pads.
Thinner disc=thicker pad.
There should be an adjustment on the piston on the better brands to retract the piston for new pads.