yeah... it is always recommended to do a full wipe..

do titanium backup and nandroid backup...just in case...

1. advisable to back up.. (sms and whatsapp)
2. sync your contacts with google contacts so that your phone numbers wont be lost. you may check your contacts at https://www.google.com/contacts/
3. backup your files (images,vids,etc)

after that you may perform flashing.
however, just because you've done flashing doesnt mean its completed.

learn about flash counters, yellow triangle issues (if happen), and learn how to use CWM (recovery).
everything can be absorbed on xda!

no prob. nothing is easy at first.
just take the initiative to learn from xda. 

people here can advise, but at the end of the day the phone is yours..
if you really screwed up, there's nothing we can do.

but if you learn the basics of it, you have high chance of preventing it from happening.

Adoii..put your backup files in your external sdcard la. Next time if you do factory reset..you backup not lost 

Planning to get to JB, so using the OTA option.

Downloaded fine. Went to start the install process, everything looking good.

Then about halfway through the progress bar where the little green android is laying down with its hood open, I get a red exclamation mark. And everything stops.

Restarted and everything is fine, but still in 4.0.4.

What went wrong actually?   

not the first time ive had it. i think its been three to four times now..   
ive downloaded it in way faster net connection before and the problem persists. as for this latest attempt though, yea, its rather crappy broadband, admittedly.

what options do i have then? upgrade firmware via kies stuck at 99% download

guys.. wanna ask.
why u guys have some problem with wireless after updating to jellybean?
cause i have unstable wireless on the phone when connected to home network.
meanwhile my iphone is having NO ISSUE AT ALL

this one you have to test on your own.

different location reacts to the baseband differently
some locations might be good, some might not.

so its best you test it on your daily route/locations or places you always go..
if the baseband is very weak, move on to the next..

its the only way you can test. so you might have to flash 4 times. (but you no need to wipe, so no worries. just choose a different modem everytime u flash without wiping)
only wipe cache and d/cache!

time for V23