Replacement of default PHP by version 5.6 installation (simplest):
yum-config-manager --enable remi-php56
yum update
Parallel installation of version 5.6 as Software Collection (x86_64 only):
yum --enablerepo=remi install php56
Replacement of default PHP by version 5.5 installation (simplest):
yum-config-manager --enable remi-php55
yum update
Parallel installation of version 5.5 as Software Collection (x86_64 only):
yum --enablerepo=remi install php55