Retourner can be used with avoir or être in Le Passé Composé... and changes meaning

Most verbs use either avoir or être as the auxiliary verb in Passé composé (or other compound tense)but retourner uses both, depending on its grammatical usage* and what it means in the sentence.
 
*Grammaphile's Corner : the technical grammatical distinction between these cases is actually whether the verb is used in a transitive or intransitive manner. 
- The transitive version (the version with a direct object) uses avoir.
- The intransitive version (lacking a direct object), uses être.

être + retourné [quelque part]

= to go back [somewhere]
= to return [somewhere]

Je suis retourné dans le village où je t'avais rencontré.I returned to the village where I had met you.

C'était tellement amusant qu'il y est retourné plus tard.It was such fun that he went back later!

Note that in each case where être is the auxilliary, the verb retourner is followed by a preposition (en, sur, dans, à etc.).  
So, in these cases retourner is usually about going back somewhereor returning somewhere.

See also Agreeing past participle with subject's gender and number with (+ être) verbs in Le Passé Composé

ATTENTION
Retourner means to go back / home whereas revenir means to come back.

 

avoir + retourné [quelque chose]

= to turn [something] upside down
= to turn [something] inside out 
= to turn [something] back to front

J'ai retourné ce pull parce qu'il gratte.I turned this jumper inside out because it itches.

Il a retourné sa casquette pour faire cool.He turned his cap back to front to look cool.

Tu as retourné la poubelle pour trouver tes clés!You turned the bin upside down to find your keys!

When retourner is followed immediately by a noun (as opposed to a preposition), it uses avoir as the auxiliary, like most verbs.   
ATTENTION: 
Retourner never means to return (something) in the context of a shop for example.
In French, we use rapporter (to bring back) or échanger [quelque chose] instead:
Elle a rapporté cette jupe comme elle était trop petite.She returned this skirt as it was too small.
  
 
Here is the list of all "two-auxiliaryverbs in compound tenses:
 

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Examples and resources

Tu as retourné la poubelle pour trouver tes clés!You turned the bin upside down to find your keys!
C'était tellement amusant qu'il y est retourné plus tard.It was such fun that he went back later!
Il a retourné sa casquette pour faire cool.He turned his cap back to front to look cool.
Elle a rapporté cette jupe comme elle était trop petite.She returned this skirt as it was too small.
J'ai retourné ce pull parce qu'il gratte.I turned this jumper inside out because it itches.
Je suis retourné dans le village où je t'avais rencontré.I returned to the village where I had met you.
How has your day been?