I want to upgrade my HDD and keep everything on it, games, account trophies etc. Is that possible or what can I do ? I don't want to lose all my game progress either.
Your account information and trophies are stored on the PSN servers, not your HDD.
Do a full backup of your HDD, replace it, restore your backup and then log in with your existing PSN ID. Everything will be as before, except you'll have a bigger HDD with more free space (until you fill it )
you will need an external HD use the backup utlility on the PS3 to backup all your saves, you can also backup your movies you bought from the PS store
however there is no way to backup the games you downloaded BUT those purchased games can easily be downloaded again for free from the store once your setup