Look at the caliper and you should be able to see 2 small indents where the pins reside flush to the caliper surface.
Both pins are hammered in horizontally through the body of the caliper till they are seemingly flush to the surrounding surface.
To remove them, you knock them out from the front (with just a punch) and they should eventually move out to the back.
The 2 pins support a retaining clip which holds the pads.The clip has to be removed before you can swap the pads out.
Fitting is reverse.Pads in, fit retaining clip, then hammer pins in from the back of the caliper.