Sure. Just sync your sources.
What I do is create a ports-supfile for syncing my OS sources. I call it ports-supfile.os. You can cut and past this if you want to:
*default release=cvs tag=RELENG_5_4
*default delete use-rel-suffix
# If you seem to be limited by CPU rather than network or disk bandwidth, try
# commenting out the following line. (Normally, today's CPUs are fast enough
# that you want to run compression.)
## Main Source Tree.
# The easiest way to get the main source tree is to use the "src-all"
# mega-collection. It includes all of the individual "src-*" collections.
# Please note: If you want to track -STABLE, leave this uncommented.
Now save the file. Then
cvsup -g -L 2 ports-supfile.os
It will download the newest sources for you. Then in this order:
# make buildworld
# make buildkernel
# make installkernel
You'll need to recompile your kernel, which this will do for you. But these steps will re-compile a GENERIC kernel. Which most likely does not include support for like example...your sound card. I always have to go back in and edit GENERIC and re-compile with optoins in for my sound card.