Upgrade system

You should make use of "freebsd-update" utility to upgrade your system non-periodically to keep your system safe and not stale. E.g., after installing a fresh 10.3 version:

# freebsd-version -ku
10.3-RELEASE
10.3-RELEASE   

You should update the patches released by FreeBSD team:

# freebsd-update fetch install

When it is done, check the system version again:

# freebsd-version -ku
10.3-RELEASE-p4
10.3-RELEASE-p5

Yeap! your system is refreshed now!

References:
FreeBSD Man Pages;
What are the first commands I run after installing FreeBSD? Or How to patch FreeBSD? Or How to install ports on FreeBSD?.