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:
https://www.youtube.com/watch?v=CQmSTQM0z8w
Watch this video to see how to replace a rear brake caliper https://www.youtube.com/edit?o=U&ar=2&video_id=czgv2kXwevA
My video using a Disk Brake Caliper tool to seat a rear brake caliper piston :
https://www.youtube.com/watch?v=eRAF_6qwGbY