Raspberry Pi Forums

If i have 2013-05-25-wheezy-raspbian.img installed and I keep it updated.
Then 2013-09-25-wheezy-raspbian.zip comes out. Do I reinstall?

You can update the kernel with
sudo apt-get install rpi-update
sudo rpi-update
sudo shutdown -r now

Coming soon is an upgrade from Raspbian Wheezy to Raspbian Jessie.
That will be a process run on your running system to update it in place.