Installing 10.0 over an 8.0 from memorystick

[Christoph P.U. Kukulies]

Quite a while ago I installed FreeBSD 8.0 on a (66GB) partition of my 
Dell notebook.  It served its purpose but
recently I wanted to use it to dump some stuff to a SD card and I found 
that 8.0 didn't detect the SD card (mmc ?).

Anyway, I thaought it could be time for an upgrade anyway and now I'm a 
bit hesitant to install FreeBSD 10.0 right from the
USB-stick (which I booted). The installer found ad0 as the disk to 
install and when I watched the disk layout
it showed ad0s3 as a BSD partition with ad0s3a as root and ad0s3b as 
swap IIRC.

What would happen, if I commit the install? Can I do better an upgrade? 
I would like to preserve my WLAN, IP and other settings.

Any advice here?

Thanks.

--
Christoph