You'll probably get better response if this were posted in the
Bicycle Mechanics section. This section is more for forum issues/assistance than bike maintenance/repair assistance.
But to answer the questions:
1) yes, you can change them.
2) go to your local bike shop and purchase a pair of pedals of the type you desire. Apply a small amount of grease to the threads and thread them into the cranks. Tighten them down with a wrench/spanner.