HELP NEEDED: downgrade from CM11 to CM10.2 - CWM 6.0.4.7 - installation error topic

Hello everyone
I have a S3 i747M, been using it stock ROMs for an year or so.
it was running on 4.4.2 KitKat, official update.

I rooted it a few days ago, installed clockword recovery touch 6.0.4.7 and installed CYANIDE-L CM11 LOLLIPOP ROM.
Which was fun until some things like the browser and chrome crashed and specially the camera doesn't like to work smoothly.

so I decided to install CM10.2 stable from the cyanogen website and ran into problems:

1 - wiped data/cache

2 - ran installer using the install zip from sdcard option - error: STATUS 7 - INSTALLATION ABORTED

looked up on the internet regarding the problem - found a fix that includes deleting bootloader? check program codes using NOTEPAD++ from the "updater-script" file in the directory "cm-10.2.1-d2att\META-INF\com\google\android".

3 - did the above mentioned fix, made a zip file - ran installer again -

got ERROR: INSTALLING UPDATE / INSTALLATION ABORTED.

4 - re-zipped the file using winzip -

ERROR: E: footer is wrong -- E : signature verification failed ---
QUES: INSTALL UNTRUSTED ZIP--- i press YES ---

ERROR: INSTALLING UPDATE / INSTALLATION ABORTED

I have searched a lot - changed the CWM version too but, no go.
Am I doing something wrong?
What can I do to install CM 10.2 - I need a stable but FAST phone, stock ROMs are dead slow.