Enter the path where you have Prestashop installed and run as the following:
cd cache/smarty/compile
find . -maxdepth 1 -type d ! -path "." -exec rm -rf {} \;
cd -
cd cache/smarty/cache
find . -maxdepth 1 -type d ! -path "." -exec rm -rf {} \;
cd -
find . -maxdepth 1 -type f ! -path "." -exec rm -f {} \;