[CentOS] In centos, how to switch to default gcc after switched to a higher version of gcc with devtoolset.

Sat Dec 1 03:03:54 UTC 2018
yf chu <cyflhn at 163.com>

I want to install several gcc with different versions in centos. The default version of gcc in centos6 is 4.9.3. So I use devtoolset install a higher version of gcc. Then I switch to the higher version of gcc by executing "source /opt/rh/devtoolset-5/enable". But now if I want to switch back to the default gcc, how should I do? 
By the way, is there any solution to install multiple gcc with different versions in centos 5?