You must bleed brakes whenever air is introduced into a vehicle brake system. This can be done by yourself ; using the method in this video.
How to use a ratchet and socket set:
   • How to use a ratchet and socket set  

Watch this video to see how to replace a rear brake caliper https://www.youtube.com/edit?o=U&ar=2...

My video using a Disk Brake Caliper tool to seat a rear brake caliper piston :
   • Using a Disk Brake Caliper tool to se...