Carefully, pry down one end of the metal holder. Push out the rubber pad. Push in the new rubber pad. Bend the metal end back in place.

I had them angled in a bench vise to do the pushing in and out. The head of the threaded bolt protrudes slightly, which is why the center of the pad is recessed; this will slightly obstruct the pads as you push the old one out and new one in.

If you manage to break off the end tab completely, just do as above and orient the tab so the braking direction is towards the remaining tabbed end.

There's no need to bend or manipulate a tab. The old pad is pried out, and often just by gripping with a slip joint plier and leverage.

The new pad is installed by starting one long side in and then with a flat blade screwdriver, work the other side of the rubber -to fully insert.

Work with patience, carefully but firm. I've done many.

Excellent choice with Kool Stop

+1 on the patience part.
You will use swear words.

With all due respect to vintage cyclist, absolutely don't do this! I did this many years ago and the aluminum holders snapped off. After buying Superbe pads from Koolstop a year ago I simply pried out the pads with a screwdriver and then pressed them back in with a woodworking clamp. Easy peasy! No bending of metal necessary. I do note that you said Superbe Pro pads, which (at least for the later generation) are rounded at the end. However the photo posted suggests that we are talking regular Superbe pads, or first generation Superbe Pro.