That's a good question, as I had the same confusion when I first
upgraded.  Basically, the installer automates 4 major steps: Install the
WAR, install a servlet engine (Jetty), install the database (HSQL), and
install the XAR.  So upgrading overtop of the installer is really not
much different from upgrading overtop of a manual install.  It would be
a good idea to familiarize yourself with the manual install procedure to
better understand what's going on; it's really not terribly confusing or
complicated.
(That being said, the last time I attempted to upgrade, I must have
messed something up, as my history stopped working, but I'm pretty sure
that happened for other reasons.)
I thought about editing the wiki page to clear this up, but I couldn't
figure out a decent way to word it.  If someone else would like to take
a stab at it, I'd love them for it.
Paul D. Grodt
TECORE Wireless Systems
  -----Original Message-----
 From: users-bounces(a)xwiki.org [mailto:users-bounces@xwiki.org] On 
Behalf
  Of Yin Kee Yee
 Sent: Tuesday, November 27, 2007 10:23 PM
 To: users(a)xwiki.org
 Subject: [xwiki-users] How to upgrade xwiki 1.1.2 stable to 1.1.2
 milestone2?
 Hi,
 I search and read through the upgrade info from this link below.
 
http://www.xwiki.org/xwiki/bin/view/AdminGuide/Installation#HUpgradingan
XW
  ikiInstallation
 It said that the general strategy for upgrade is to download the WAR
 Distribution and to replace your current installed WAR.
 Since I did an initial xwiki install using the standalone xwiki 
enterprise
  window 1.1.2 installer, how can I upgrade to 1.1.2
milestone 2 without
 losing any current data? To be more specific, which file should I 
download
  and use?
 Thanks,
 YinKee