1. i'm asking to avoid to brick the phone choosing the wrong sbf
2. I already did it, but i dont remember anymore what i used last time,
and there are a tons of options and i dont know what is the right one
3. you right i noted too late and i dont know if i can move the post in Q&A
Well, to topic:
When you're on CM10 and want to start all over, you must tell the forum, where exactly you plan to go.
Example: you want a fresh install of CM10, then you do not need to flash sbf at all.
Example2: you want to go to CM7, then you need *maybe* (look inside the threads of the ROM you are going to use!) a fresh sbf. You should NOT take an sbf which upgrades your bootloader (BL).
This is the thread where you can find out what sbf comes with which bl version. You can flash any sbf which comes with the same bl version you have, without problems, just pick your flavor, language, and choose the right one for defy red lens.
And
this is the FAQ thread for installing Quarx' CM10.
If you want a "clean" install just wipe data as point 2. before flashing.
You find it at:
► I already have CM10 and I want to upgrade to a newer nightly, how can I do that?
Manual update:
1) Go to Recovery
2) Wipe Cache and Dalvik
3) Flash the last .zip file.
4) Flash gapps (just if you have a newer version of gapps, otherwise, this step is optional)
4.1) (ONLY DEFY RED LENS WITH PRE 2ND BOOT BUILDS) Flash battery fix (if you don't, the battery meter will display 1%)
5) Wipe Cache and Dalvik (this is also optional)
6) Restart.