If you've accidentally installed the wrong repo as long as you haven't used it you are safe, if you have ran a upgrade with the wrong repo you could be in trouble.
How to remove Epel / Remi for Centos 7:
rpm -e remi-release-7.0-1.el7.remi.noarch
rpm -e epel-release-7-5.noarchHow to remove Epel / Remi for Centos 6:
rpm -e remi-release-6.5-1.el6.remi.noarch
rpm -e epel-release-6-8.noarchNot the latest ones just run the following commands:
rpm -qa |grep -i remi
rpm -qa | grep -i epel