How to switch GCC version on Ububtu

I had installed GCC version 4.9 and 5.4 from the Ubuntu repositories. How to switch GCC version?
You can switch the symlinks yourself manually, but using "update-alternatives" makes it easy.

[ ]$ sudo update-alternatives --install /usr/bin/gcc gcc /usr/bin/gcc-4.9 100 --slave /usr/bin/g++ g++ /usr/bin/g++-4.9
[ ]$ sudo update-alternatives --install /usr/bin/gcc gcc /usr/bin/gcc-5 50 --slave /usr/bin/g++ g++ /usr/bin/g++-5 

Now you can switch between these versions by using:

[ ]$ sudo update-alternatives --config gcc

Change GCC 9 (Ubuntu 22.04)

[ ]$ sudo apt install gcc-9
[ ]$ sudo update-alternatives --install /usr/bin/gcc gcc /usr/bin/gcc-9 100