$ yum install [packagename].x86_64
This way you will specify the architecture to use. If you do not specify the architecture you might end up installing both the x86_64 and the i386 packages with all it's dependencies.
If you have already done so in error, you can easily query for these packages using the following command:
$ rpm -qa --qf '%{name}.%{ARCH}\n' |grep i386
this command returns all i386 packages. You can pipe it directly into rpm -e or choose to uninstall them by hand.
