Difference between 4.0.3 and 4.0.2?

[Carnage]

what does this mean? does it mean i lose all changes? or does it mean i need to restore them to default before i upgrade?

What it means is that there have been changes to those templates in order to fix bugs. If you do not get the changes made in those templates into your template, there may be issues with your site.

You don't have to revert before upgrade as there is the template merger which is supposed to carry your changes over however it doesn't always work, depending on how and what you have customised. You may loose some of your changes or have to merge the templates manually.

I would suggest you copy your current database and board to another location and perform a test upgrade on that to see how well it works before attempting it on your production board.

and how do i go about upgrading? do i need to pay? is it worth the upgrade?

Make a backup; theres a lot of resources on vbulletin.com and here that show you how to do that.

Similarly to installing in the first place; first download the latest release from the members area, then upload the files to your website; ensure that you allow it to overwrite the files that are already there, then goto www.yoursite.com/install/upgrade.php follow the instructions. Delete the install dir from your server and review the merged templates.

You will only need to pay IF you have an old style vbulletin 3 liscense which you haven't upgraded to a new style vbulletin 4 liscense and it has expired. If you bought a vbulletin 4 liscense, the update is free.

It is defiinatly worth it; somewhere between 250 and 300 bugs were fixed for this release and it added facebook connect to allow members to login and regiser with their facebook account (this is disabled by default thou, so you'll have to set it up as per the instructions if you want to use it)