Entropic template
 

My character just acquired the Improved Familiar feat, and I am trying to upgrade my Parrot familiar to an Entropic Parrot.

I see I can add the Celestial or Fiendish templates as class levels, but do not see similar options for the Entropic template (or the Resolute template, for that matter). I have all of the Bestiary data packages in my license.

Do you have Bestiary 2 turned on? (Ctrl-K) and scroll down to make sure you have it checked. Both of those templates are in B2, and both are present when I look for them.

I do now.
 

That was it, thanks!

For anyone else who might face this issue: I created my character before I bought the license for the Bestiary packages, so the rulesets were turned off. After I bought the license, I turned the rulesets on at the opening screen where it asks you to create a new character or gives you the option to load a new character. What I did not realize, but just discovered, is that you need to turn on the rulesets on a per character basis -- turning them on at the opening screen does not turn them on for a character that was already created.

Correct. They will be turned on for future characters (unless you change your defaults), but for existing files that were made before the license, you will need to turn it on.