Alter a character in all files in a directory and sub folders

[Trob70]

I have a large number of files in a root folder with sub directories eg f:\fixxml\ (this contains sub folders with .xml files as well)
I need to alter a character in the files eg ’ to '
Have never used powershell before..!!!

Did try the following with no success
in cmd
F:\fixxml
powershell
then this command
get-childItem *.xml | rename-item -newname { $_.name -replace '’','''} !!! does nothing !!!!

Would really appreciate a command line that will do this for me

Regards Robert