Offical upgrading is easy. And you know how to do this correct? If not theres a tutorial on that. Now to tell what build/aku u have look at the build number in the start/settings/system/about the last 3 of the build should be something like 2.0.0 that's aku2.0 mine says 3.3.0 that's aku3.3.
Nothing needs to be done prior except backup ur normal stuff emails, contacts, and what not. But do not use the pim.vol trick for the contacts.
To do the upgrade put ur ppc into bootloader mode by pressing the notes key, power button, and soft reset at the sametime. To know u done it correct. You will see a very faint word serial (unless u have the usb plugged in then it would say usb). Plug it in to ur desktop, run the maupgrade_noid.exe or whatever the extact name is. Follow the steps like a normal upgrade. But these can't be done on machines running vista and all firewalls, antivirus and what not are recommended to be turned off even the windows one.
extrom is ur extended rom, when u hard reset u see the u have 3 secs blah blah then installs all sprints or ur carriers junk and needed software for the phone to work. read more on the tutorial....
theres a huge thread with known issues so I suggest u get to reading.
Best of luck,
Mike