Convert ' to ' with php

I read the content of a site with php (and simple html dom) and there are some special characters as ' ( ’ ).

I tried to convert it with html_entity_decode($lastcat->plaintext) but I did not solve it ,what have I do to convert the text with special characters to the actual text?

Thank you

I solve it with this

html_entity_decode( $lastcat->plaintext, ENT_QUOTES )