Disable SELinux

You can manually edit the SELinux config file in /etc/selinux/config and change the variable SELINUX=enforcing to disabled

vi /etc/selinux/config

...
SELINUX=disabled
...

or you can use this little command

sed -i.bak -e 's/^SELINUX=.*/SELINUX=disabled/g' /etc/selinux/config

Enable SELinux

You can enable SELinux manually the same as above but set SELINUX=disabled to SELINUX=enforcing

vi /etc/selinux/config

...
SELINUX=enforcing
...

or

sed -i.bak -e 's/^SELINUX=.*/SELINUX=enforcing/g' /etc/selinux/config