well first i will say, 2.2 has its perks and its pretty fast but i find the latest release not as fast as previous beta's and going back onto a custom 2.1 i find the phone a great deal faster even tho quadrant scores dont reflect that.
i guess the first thing you need to do is install the flashtool:
xda-developers - View Single Post - [TOOL] [NEW 01/02/2011] Flashtool version 0.2.6
then using the flashtool, you can root your phone you do this by having your phone switched on then in the applications menu of your phone, switch on unknown sources and in the development part, switch on usb debugging.
click root in the flashtool and it should root your phone.
once rooted, you'll need to download busybox installer from the market, run that so it installs busybox on your phone.
next get xrecovery:
[RECOVERY] xRecovery 0.3-release | UNIFIED - ALL X10 VARIANTS | 31/01/2010 - xda-developers
instructions should be there but all it requires is putting the file on your sd card and then install it to your phone.
run it, and if you are rooted you should have no problems with the install.
you will also need a 2.2 rom, this one is the best one to have:
[ROM] FreeX10 | BETA 4 - NEW BASEBAND FIX | Froyo 2.2.1 | 1/02/2011 | xRecovery - xda-developers
download the beta4 file and also the x10 gapps file, put both of these on your sd card.
before you try to install these make sure your have xrecovery working, to do this reboot your phone and once the sony ericsson logo appears continually press the back key of your phone.
if all is well it will go into the xrecovery menu, would be a good idea to make a backup using the backup/restore option.
once you have made your backup, switch your phone off and take the battery out.
you will need the latest baseband:
xda-developers - View Single Post - [TOOL] [NEW 01/02/2011] Flashtool version 0.2.6
once that file is downloaded extract the file within to the firmware folder of the flashtool.
run the flashtool, it will tell you to connect your phone, once connected, click flash, it will do its thing and then it will tell you to unplug your phone then reboot it.
when you reboot it immediately go back into the xrecovery menu, DO NOT let your phone boot up.
in xrecovery, select install custom zip, then select the beta4 file from your sd card and install.
once done select reboot, your phone will boot up, might take a while and might have a few reboots before it settles.
reboot and go back into xrecovery and install custom zip and select the gapps file from your sd card, install that then go into advanced options and clear davlik cache, once done, reboot and let it boot up, again it may take a little while but that should be you on 2.2 beta 4.
if have ANY problems with this you can flash back to 2.1 using the flashtool and one of the builds listed in the flashtool thread, if you have any problems rooting then again, flashing one of these builds may help.