Trying to install Pro Version

Hi! I have followed the directions posted on the community forum and cannot remove the Smushit folder from the FTP server in order to install the Pro Version. I keep getting these commands:

Status: Deleting 4 files from "/var/www/wilsonclinical.com/public_html/wp/wp-content/plugins/Wpsmushit"
Command: rm "/var/www/wilsonclinical.com/public_html/wp/wp-content/plugins/Wpsmushit/license.txt"
Error: rm /var/www/wilsonclinical.com/public_html/wp/wp-content/plugins/Wpsmushit/license.txt: permission denied
Command: rm "/var/www/wilsonclinical.com/public_html/wp/wp-content/plugins/Wpsmushit/readme.txt"
Error: rm /var/www/wilsonclinical.com/public_html/wp/wp-content/plugins/Wpsmushit/readme.txt: permission denied
Command: rm "/var/www/wilsonclinical.com/public_html/wp/wp-content/plugins/Wpsmushit/wp-smush.php"
Error: rm /var/www/wilsonclinical.com/public_html/wp/wp-content/plugins/Wpsmushit/wp-smush.php: permission denied

Please help! Thanks!