got answer from this link https://www.digitalocean.com/community/questions/how-to-upgrade-curl-in-centos6
worked for me.
add a new text file called /etc/yum.repos.d/city-fan.repo containing
name=City Fan Repo
Either way, you should then be good to go :
yum install libcurl should update cURL to a (very) recent openSSL-based version (7.46.0 at the time of writing), which will resolve the "unknown protocol" errors for TLSv1 etc.
You may want to then remove/rename the city-fan.repo file if you want to prevent yum later also updating other packages you may have installed with "non-official" later versions.