couldn't make OS upgrade due to lot of duplicate rpm's

yes some times couldn't make it due to lot of duplicate rpm's and dependencies.

if you could see the less packages you can remove manually. using nodeps command

# rpm -e --nodeps <pkg name>

>> If the issue is with lot  of dependencies.

Then try # yum update  --enablerepo=*

Actually yum itself means install dependencies as well. But somehow very rarely it couldn't install dependencies. it might be the reason some times new version package requires older versions. So give a try with
# yum update --enablerepo=*


its works for me.