"Yum install monit" command by default will install 5.14 version. But Monit has released till 5.20 version
I tried with the below command for available packages
sudo yum --showduplicates list monit | expand
It shows up only one available package Available Packages monit.x86_64 5.14-1.el6
Are there any other option apart from manually downloading the tar using wget command and then installing it.
There used to be an RPM on the rpmforge/repoforge repos although these are presently down.
I believe these might resurface (based on this https://github.com/repoforge/rpms/issues/375) but in the mean time unless you want to build your own RPM for it you could grab this from a mirror.
Such as:
yum install https://www.insaneworks.co.jp/pub/el6/RPMS/x86_64/monit-5.20.0-1.el6.x86_64.rpm