Smush pro error

Hi,
I have connected the new site to my account, but I am getting this error when I go to activate it:
Fatal error: Cannot redeclare get_plugin_dir() (previously declared in /public_html/wp-content/plugins/wp-smushit/wp-smush.php:118) in /public_html/wp-content/plugins/wp-smush-pro/wp-smush.php on line 116

What do I need to do to activate the plugin? Thank you