Default [SONY XPERIA J] ROOT/CWM Problem switching memories

Hello, i am joaquim and this is my first post so sorry if this is not in the right place or something and I also am a beginner in this subjects..
I have a few questions..My device is a Sony XperiaJ ST26i and the firmware is 11.2.A.0.31.
My inicial intention was to switch the internal memory with the ext_card..I have a friend with the exactily same device who recently did this and was soo easy for him, just root, no CWM rename the vold.fstab with the root explorer and it was done..Well this didn't work out for me and problems started to show here..
I searched a lot and this forum was a big help but somehow I allways ended up stuck.
First I rooted the device..ok! then I wanted to install the CM10 ROM, well I couldn't :S as some topic here refered I installed on my PC the flashtool and no signs of my device in the program..still i went further and in the step that I unplug my device from the PC when I plug him back holding the "+" button the flashtool says that "usb debuging is off" and "MTP is off" and they are both turned on..but then again I don't even know if i am starting the device in the recovery mode in the right way :S
Can anybody help? Am I doing the things right? if not is there a simple way or something?
another question, should I reset my device to the inicial values to do this kind of things? and i am assuming that the ext_sdcard does not make difference if is on or off...
Ho and to root i used the Adb...
I would apreciate have this problem solved..I am stuck in this for days and have searched and searched and what works for the others allways leads me to a dead end -.- It can be a small detail that i am not seeing ...

best regards,
JM