You should do this:
cd /usr/bin
mv gcc gcc-old
ln -s gcc-4.9 gcc
Or you should have a look to gcc_select
Question
I recently installed gcc 4.9, with a previous version of gcc that was installed by default before.
When I type gcc, the previous version of gcc runs. How could I make my newly installed gcc 4.9 run when I type gcc?
Solution
You should do this:
cd /usr/bin
mv gcc gcc-old
ln -s gcc-4.9 gcc
Or you should have a look to gcc_select