If you want to install a new ROM on your rooted T-Mobile Galaxy S2 SGH-T989, you will want to make sure to make a backup of your ROM first (see How to Backup ROM on T-Mobile Galaxy S2!)
UPDATE (Nov. 14th 2013) – Please make sure to upgrade your CWM when installing Android 4.4 KitKat ROMs FIRST!
Also, installing new ROM erases all your settings and apps, I highly recommend you to use Titanium Backup app to backup your apps beforehand. (see How to Backup/Restore Apps with Titanium Backup app!)
Once you’ve got the backup of your ROM and also apps out of the way, here’s how to install ROM on a rooted T-Mobile Galaxy S2:
Step 1. Install ROM Manager off Market and open.
Step 2. Choose “Flash ClockworkMod” to install the latest version.
Step 3. Copy over the ROM zip file you want to install by putting it in USB storage mode then copying over the file on your computer.