Suse releases

I have just installed open suse 11.1 - i have a few questions.

1.) When the release of Suse goes up a level - for instance to 12. do i have to reinstall the whole os or does it update all the system via the network??

2) Is it best practice to install all software through official suse packages?

Please be patient as i have never used linux before and have been a long time windows user.

Thanks in advance