The anaconda installer will have ext3 to ext4 conversion,
however a new install will be most beneficial as the converted ext4 does not change the old ext3 blocks until they get updated into an extent area.
Even so, the f/s layout is much different with a new ext4 f/s.
I also think if you have little experience and your data is only fluffy tid-bits of star dust, you'll gain more by doing a new install and configuring it for you needs.
The fact that you are so egger to update from F10 to F11 tells me you have not important data and you don't understand Fedora, so until you have experience and knowledge, installs only, and install often, like today from the boot.iso because it's a new anaconda and it needs tested.
$ uname -a
Linux Jovette-14.WinProxy 188.8.131.52-142.fc11.i686.PAE #1 SMP Tue May 12 22:46:45 EDT 2009 i686 i686 i386 GNU/Linux
Jovette-14 ~]$ uptime
08:31:12 up 3 days, 21:20, 3 users, load average: 0.09, 0.10, 0.13
Do the Math