How do I recruit more pilots?

Should all your crewmembers fall victim to unfortunate accidents, you can always recruit more at the astronaut complex. Should the astronaut complex run out of applicants of the right class, just go to the tracking station and speed up time. After a few days new applicants will appear, eagerly waiting for you to hire them and send to heaven in the name of science.

When all your available slots for active astronauts are filled with non-pilots, you can also use the astronaut complex to sack any who are not on a mission. When the kerbal you want to get rid of is currently on a flight, you can terminate that flight in the tracking station. Any kerbals on the flight will then be listed as "Lost" in the astronaut complex and will no longer occupy a slot.

The class of an astronaut is determined when they spawn as applicants in the astronaut complex. It can not be changed.