mobile

I have an old smartphone (model specified above), which I have tried to find a root for it (like FOREVER), and misrebly failed. Every single root I found was worked for the LT18I users (as it seems in the comments), but not for me.
I want to root it so I can uninstall some of the build-in apps that I dont use (such as facebook, youtube, and out-of-date & un-updateable operator apps.). They function poorly, take up space, and worst of all: they run in the backround (and on old phones such as this every megabyte of RAM counts.) Please help me.

Is there something I'm missing? A vital step a skip or something? Do I need to unlock the bootloader to root? Or do I need to root to unlock the bootloader?
I probably have an operator's custom ROM (The phone was purchased through that operator instead of a regular electronics shop). Does this make any difference?
If Anyone can explain to me step-by-step what and how to root, or point me to a usefull guide, I will be forever thankful. Nothing worked for me so far.

Sony Ericsson Xperia Arc S LT18a
Firmware version: 2.3.4
Build:4.0.2.D.0.5