i currently run Fedora 12 with the latest stable kernel update.
Heres the command steps l took to erase the 2 kernels l dont need.
Its always a good idea to have a fall back previous kernel available if needed.

[steve@pegasus Documents]$ su -
Password:
[root@pegasus ~]# uname
Linux
[root@pegasus ~]# uname -a
Linux pegasus 2.6.31.9-174.fc12.x86_64 #1 SMP Mon Dec 21 05:33:33 UTC 2009 x86_64 x86_64 x86_64 GNU/Linux
[root@pegasus ~]# yum clean all
Loaded plugins: presto, refresh-packagekit
Cleaning up Everything
0 delta-package files removed, by presto
[root@pegasus ~]# uname -r
2.6.31.9-174.fc12.x86_64
[root@pegasus ~]# rpm -q kernel
kernel-2.6.31.5-127.fc12.x86_64
kernel-2.6.31.6-166.fc12.x86_64
kernel-2.6.31.9-174.fc12.x86_64
[root@pegasus ~]# clear

[root@pegasus ~]# uname -r
2.6.31.9-174.fc12.x86_64
[root@pegasus ~]# rpm -q kernel
kernel-2.6.31.5-127.fc12.x86_64
kernel-2.6.31.6-166.fc12.x86_64
kernel-2.6.31.9-174.fc12.x86_64
[root@pegasus ~]# yum remove kernel-2.6.31.5-127.fc12.x86_64
Loaded plugins: presto, refresh-packagekit
Setting up Remove Process
Resolving Dependencies
–> Running transaction check
—> Package kernel.x86_64 0:2.6.31.5-127.fc12 set to be erased
–> Finished Dependency Resolution

Dependencies Resolved

================================================================================
Package Arch Version Repository Size
================================================================================
Removing:
kernel x86_64 2.6.31.5-127.fc12 installed 98 M

Transaction Summary
================================================================================
Remove 1 Package(s)
Reinstall 0 Package(s)
Downgrade 0 Package(s)

Is this ok [y/N]: y
Downloading Packages:
Running rpm_check_debug
Running Transaction Test
Finished Transaction Test
Transaction Test Succeeded
Running Transaction
Erasing : kernel-2.6.31.5-127.fc12.x86_64 1/1

Removed:
kernel.x86_64 0:2.6.31.5-127.fc12

Complete!
[root@pegasus ~]# rpm -q kernel
kernel-2.6.31.6-166.fc12.x86_64
kernel-2.6.31.9-174.fc12.x86_64
[root@pegasus ~]# yum remove kernel-2.6.31.9-174.fc12.x86_64
Loaded plugins: presto, refresh-packagekit
Setting up Remove Process
Resolving Dependencies
–> Running transaction check
—> Package kernel.x86_64 0:2.6.31.9-174.fc12 set to be erased
–> Finished Dependency Resolution

Dependencies Resolved

================================================================================
Package Arch Version Repository Size
================================================================================
Removing:
kernel x86_64 2.6.31.9-174.fc12 installed 98 M

Transaction Summary
================================================================================
Remove 1 Package(s)
Reinstall 0 Package(s)
Downgrade 0 Package(s)

Is this ok [y/N]: y
Downloading Packages:
Running rpm_check_debug
Running Transaction Test
Finished Transaction Test
Transaction Test Succeeded
Running Transaction
Erasing : kernel-2.6.31.9-174.fc12.x86_64 1/1

Removed:
kernel.x86_64 0:2.6.31.9-174.fc12

Complete!
[root@pegasus ~]# rpm -q kernel
kernel-2.6.31.6-166.fc12.x86_64
[root@pegasus ~]#