0. I've been burned enough times to do this out of habit: make a backup of /etc/grub.conf, retaining SELinux info:

# cp --preserve=context /etc/grub.conf /etc/grub.bak

1. Add biosdevname=0 to the kernel boot arguments in /etc/grub.conf.

2. Rename /etc/sysconfig/network-scripts/ifcfg-em1 to /etc/sysconfig/network-scripts/ifcfg-eth0, changing the line

DEVICE="em1"

to

DEVICE="eth0"

3. Delete /etc/udev/rules.d/70-persistent-net.rules

4. Reboot.