My advice is always this: if your device is working as you wish and need, then it isn't broken and doesn't need to be fixed with an OS upgrade. Our forum is full of problems with upgrades, but on the other hand, we rarely get the "upgrade went great" discussion.
And if you have apps, themes and ringtones that you like and use with your current OS, keep in mind that they may not work with the upgrade, particularly going from OS5 to OS6.
If you decide to continue, see the yellow sticky at the top of the 9300 for the latest OS version and the instructions. Follow them exactly and have patience since it can take an hour or longer. And make sure that you have a good back up of your data and also sync with Outlook, Google or whatever you use.