C-Lightning update 0.6 doc How do you update safely to 0.6 the working C-Lightning node?
You should be able to just stop the old version, download the new binaries, unpack them, and run them. On the first start lightningd will take care of updating the database if necessary and 

Alternatively you can also compile the binaries yourself, like you did before the release:

git clone https://github.com/ElementsProject/lightning.git /opt/lightning
cd /opt/lightning
./configure --disable-developer --disable-valgrind
make 
sudo make install


Afterwards lightningd and lightning-cli will be in your $PATH and available from everywhere.