Portupgrade
Portupgrade is a useful tool for updating particular ports. Easily installed from the ports:
cd /usr/ports/ports-mgmt/portupgrade
make install clean
Now create a database:
pkgdb -F
Now, to upgrade clamav for example, simply run:
portupgrade clamav
Note: It is important to regularly update the package database using pkgdb -F to fix inconsistencies, especially when portupgrade asks you to. Do not abort portupgrade while it is updating the package database, this will leave you an inconsistent database.