@Ma3loom,
I'll try, I had multiple pages open, and was using a little bit of everything...
Brief Summary:
Rooted, cleared cache, factory reset, downloaded image of tmo ics, used Odin to flash the tmo ics rom onto phone, rooted again(not sure if this was necessary, but I did it anyway).
Remove your sd card, copy/move all your files, basically backup what you don't want to lose.
1. -root.
How to Root ICS/GB on T-Mobile Galaxy S2 SGH-T989! | Galaxy S2 Root
2. -clear cache. I did a darkside superwipe, but that soft bricked my phone. So I had to reinstall ics, but I'm super glad I did. You can clear cache when your in one of the 2 types of modes, (when you hold down the vol up/down button and get into the weird modes, one of the 2 modes has a clear cache option-go back to the rooting guide to get to it.)
3. -install new image. Download the image, use Odin and flash the new rom. (I downloaded an image from the tmobile.com forums, but this should be the same)
(ODIN)(ICS)(LE1) SGH-T989_TMB_1_20120608172207_ugy1nehf4g - xda-developers
4. - I started the phone, then did a factory reset, not sure if this is necessary.
5. optional, install Titanium backup, it costs money, but it was the first app I bought, it's worth freezing unnecessary stuff.
I also use setcpu, and underclock my cpu,
If anything doesn't make sense, pls look it up online or on xda, as I did.
Apps I have installed:
Titanium Backup -freezing/deleting apps, I suggest freezing
Setcpu - underclock your cpu, battery saver, it's dynamic, so the cpu mhz will ramp up when you need it
Clockwork mod, not sure when I got this, probably when I first rooted, that was on Gingerbread.
Other resources.
XDA forums, tmobile.com forums.
Like I said it's a pain, but it's worth it.
Downloading the image was the longest part of the ordeal, had to wait 45 minutes to download...
My reason for reimaging...
I downloaded ics via kies, phone was laggy, not responsive, I cleared my cache, that created another issue where it got stuck at the goodbye screen, so that didn't help, so I super cleared my cache using darkside, that made my phone not even boot, it was stuck at the loading screen. So I got into download mode, installed the new Tmobile ICS image/rom, and everything has been great since then.